Competing in a bodybuilding contest can be a source of immense physiological and emotional stress. As one of the most demanding activities one can engage in, it requires extreme control, discipline, and motivation to even be competitive in the sport. To recover from this stress and bring the body back into balance, attention to proper nutrition and supplementation is critical.
Further suggesting that training to failure plays a lesser role in the hypertrophic response is a study that noted that training to failure with light weight did not produce marked strength gains (meaning that failure itself wasn't the most critical factor).[6] In fact, increasing the resistance of the movement recruits more motor units and is correlated with gains in strength and hypertrophy.[6,7]
Change things up. After six or more weeks of consistent strength training, which is about the amount of time it takes to start seeing improvement in your body, you can change your routine to make it more difficult. Lifting the same weights for the same exercises every week will keep your body in the same place. You can modify weights or repetitions, choose different exercises, or change the order in which you do them. You only have to make one change at a time to make a difference, although more is often better. 
JDB, great tip on cardio before weights. Having trained in a boxing gym for years, this is exactly how I would start each training session, even if I was going to focus on weights that day. Use to start off, 3-4 rounds on jump rope in the ring, alternating between fast high knees and then slowing it down. It was all continuous for about 10-12 minutes. Would then continue w basic calisthenics (mountain climbers, bw squats, burpees, etc.) for another 3-4 rounds. This was all done w boxing timer running in background. Would finish “warm-up” w some kind of pull-up/chin-up, dips, and hanging abdominal work. Then it was time for weights. This just overall improved my general conditioning/movement and never felt that my strength diminished when doing this. Actually, felt stronger due to increased blood flow.
Don't worry, we're still talking snail's pace weight gain. Aim for one pound per week of lean muscle mass gains, though you may initially gain faster if you started out extremely lean or glycogen depleted. Start by adding 500 calories to your current daily intake, and maintain that intake until you plateau. If or when this happens, add another 250-500 calories and repeat.
You should also have everything you need for simple workouts. Especially if you plan to hit the gym nearly every day, it's a good idea to have some equipment for those rainy days when leaving the house isn't an option. And let's face it: Buying some basic workout items will make your jump into the fitness world more fun. This might sound trivial, but having clothes you like can influence your desire to train.
In addition, work on incorporating healthy foods with essential fatty acids into your meals. Though the word fat can scare away aspiring bodybuilders, remember that obtaining a certain amount of essential fatty acids can actually benefit your body and help you build muscle. Just as essential amino acids aid our bodies with growth and good health, our bodies require us to consume two primary essential fatty acids in our diets: linolenic acid and linoleic acid. So as you prepare your diet, consider which foods are a good source of these essential fatty acids. For example, chicken fat contains more linoleic acid (about 20%) and lenolenic acid (0.8%) than beef.

It is quite difficult to achieve competitive success without proper supplementation. For example, you could easily replenish your carbs on an Ironman course with white bread and Fig Newtons, but you'd have to carry a backpack full of the stuff to ensure your calorie intake was adequate. It's much easier to supplement with a carb/sodium replacement gel.
There are some things on here that you can do from home if you own the equipment, such as I do, but there are some things you cannot do without going to a gym… because who really owns a Leg press in their home? That is why there are alternatives to almost ANY exercises such as using resistance bands instead of cables for the cable curls, etc. Tweak the program to best suit your needs!
Familiarize yourself with important muscle groups and basic anatomy. Bodybuilders are part athletes and part artists. Like a sculptor uses clay or marble, a bodybuilder uses sweat and determination to train the muscles and sculpt the body into a particular physique. Planning what you want to get out of bodybuilding, how you want to shape your body, is a big part of the process. Get the following textbooks to do your research on the body:
Traumatic-sounding, but true: muscle damage — or more specifically, the micro-trauma to muscle and connective tissue that’s a natural consequence of resistance training — touches off a regenerative process that can stimulate the production of new muscle cells. Research shows that eccentric movements (e.g., the lowering phase of a bicep curl), which require a muscle to lengthen under tension, produce greater micro-trauma than concentric movements (e.g., the lifting phase of a bicep curl), which require it to contract.
One of the basic tenets of weight lifting: you must either add weight, add sets, increase intensity or decrease rest time to encourage continued progress. At this stage, adding weight makes the most sense and will be recommended throughout the first 6 months or so. But by the very nature of acquiring experience, you'll also be adding sets. Decreasing rest time and the use of intensity techniques is used as you reach strength plateaus, when you are more advanced.
Attend local competitions. When you are just starting out, visiting local competitions will be helpful for a few reasons: you will be able to get a feel for competitions and what will be expected of you, you will be exposed to your potential competitors, and you will be able to speak with like-minded men and women who also enjoy the sport. You can make connections at a competition you might not be able to make at your local gym.

It's OK to be a little sore. Your muscles might feel achy or tired the day after a tough training session thanks to DOMS, or delayed onset muscle soreness. When you strength train you're causing microscopic damage to the tissue that will be repaired, that's how you build stronger lean muscle. Speaking of repair and recovery, though, rest days are important. "If you constantly break down muscle without a recovery period, you won’t give the muscle fibers a chance to repair and build back stronger,” explains Davis.
10 week mass building program. This workout is designed to increase your muscle mass as much as possible in 10 weeks. The program works each muscle group hard once per week using mostly heavy compound exercises. You will train on a 4 day split routine, resting on Wednesdays and the weekends. To get the most out of this program you need to be eating BIG. Big meals, at least 5 times a day.
Shorter rest periods have their place — especially if your goal is muscular endurance and fat loss. But longer rest allows you to perform more reps on subsequent sets, and this greater volume, over time, may lead to greater muscle gains in the long run. One convenient way to do this without tacking additional time onto your bodybuilding routine: Perform supersets, which are back-to-back sets of two different exercises that target non-competing muscle groups (e.g., the squat and biceps curl, or the bench press and bent over row).
Training to a point of momentary muscle failure, at which completion of another repetition on any given set is impossible despite your greatest effort, is the only way to force the body to resort to its biochemical resources sufficiently to stimulate real growth! One of the biggest mistakes I see being made in the gym is when certain individuals will end a set of an exercise just because an arbitrary number of repetitions has been completed.This will do very little to stimulate muscle growth. A set should be terminated only when your muscles have been forced to the point of it being inconceivable to produce 1 more repetition within a working set. I use the word forced because obviously, you know muscle growth doesn’t come easy and literally needs to be forced! Any degree of effort in a set that is less than 100% may yield a bodybuilder some results, but never to the same extent that all out maximum effort will.
The most important aspect of your bodybuilding diet is calorie intake. To build mass, you need between 20 and 22 calories per pound of body weight each day, according to sports scientist Jim Stoppani. This would mean a 150-pound beginner bodybuilder would need between 3,000 and 3,300 calories per day to gain weight. Stoppani advises reducing your intake slightly on nontraining days, though, as you're less active. On these days, aim for 18 calories per pound, meaning the 150-pound bodybuilder would need 2,700 calories on rest days.
As a result, the Old School bodybuilding meant relying on the basic movements using primarily barbells and dumbbells to develop their physiques. This lack of variety turned out to be a blessing in disguise as the free weights helped to build greater muscle mass and strength compared to the more sophisticated equipment that was yet to come. Barbells and dumbbells required to body to utilize greater coordination and balance in order to perform the movements. The result was increased strength and size, much more pronounced than when machines are used.
Attend local competitions. When you are just starting out, visiting local competitions will be helpful for a few reasons: you will be able to get a feel for competitions and what will be expected of you, you will be exposed to your potential competitors, and you will be able to speak with like-minded men and women who also enjoy the sport. You can make connections at a competition you might not be able to make at your local gym.
The high levels of muscle growth and repair achieved by bodybuilders require a specialized diet. Generally speaking, bodybuilders require more calories than the average person of the same weight to provide the protein and energy requirements needed to support their training and increase muscle mass. In preparation of a contest, a sub-maintenance level of food energy is combined with cardiovascular exercise to lose body fat. Proteins, carbohydrates and fats are the three major macronutrients that the human body needs in order to build muscle.[24] The ratios of calories from carbohydrates, proteins, and fats vary depending on the goals of the bodybuilder.[25]

Training intensely is the key to stimulating muscle growth but don’t mistake volume for intensity. All too often, people trying to achieve a higher level of intensity in their training make the mistake of assuming that increasing volume and duration are effective methods of boosting training intensity. Let me make this perfectly clear. Volume and frequency have absolutely nothing to do with intensity! High volume training sessions can actually be counter-productive. So how do you effectively increase intensity? A. By progressively increasing the amount of weight that you use. B. By progressively decreasing the amount of time it takes you to perform a particular amount of work. (For example, I have made some of my best muscle gains from workouts that lasted no longer than 30 minutes.) C. By working your muscles at the capacity of nothing less than 100% on every set.