If you have little experience of weight training and free weights, you may wish to start with the machine leg press instead of the squat, especially if you're not accompanied by a trainer, helper or spotter. Even so, there is no reason to be intimidated by the squat exercise. It need not be done in a squat rack or power cage with the big bar and free weights to begin with, although squatting with the bar alone is a good way to practice form. Dumbbells or small-bar barbells or a Smith machine can provide reassurance for the beginner. The same applies to the racked bench press with heavy bar, which can be substituted with dumbbells or lighter barbells. The key is not to lift too heavy too soon.

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.

Use protein supplements wisely. Throwing back a protein shake every morning is not a guarantee that your body will build muscle mass. Although protein shakes are not inherently bad, they are also not a magical means of building muscle. If you decide to implement a protein supplement in your diet, make sure the ingredients are high-quality (i.e. not riddled with sugar and empty carbs).[13]

To get the most gain from resistance training, progressively increase the intensity of your training according to your experience and training goals. This may mean increasing the weight, changing the duration of the contraction (the time during which you sustain holding the weight at your muscle’s maximum potential), reducing rest time or increasing the volume of training.
At the end of the day, you have to focus on how you feel. “Listen to your body,” says Davis. “It tells you when it needs a day off.” As a rule of thumb, take a rest day if your perceived pain is above a seven on a scale of 10, Davis advises. Or, focus on a different body part (say, if your legs are sore, focus on upper-body moves). Can't stop, won't stop—at least, till your next rest day.
Consult a nutritionist. Everyone has a different metabolism and will require slightly different supplementary nutrition for building muscle. It's a good idea to meet at least once with a nutritionist or other health counselor to build a diet plan specifically tailored to your body and what you want to do with it. It's impossible to give a single, generalized diet plan that will work for everyone, so you'll need one specific to your needs.
To achieve healthy fat loss, the best prescription is moderate calorie restriction combined with physical activity. Try to reduce your intake by no more than 30 percent of your total calories. Never go below 70 percent of maintenance intake. For example, if you've been maintaining weight on 2,000 calories, try to get at least 1,400 calories while dieting.
General nutrition: Experts advise sticking with healthy, nutrient-rich foods as part of a weight-gaining diet (rather than loading up on caloric, but not nutritious, foods such as candy, chips, and soda). They may also suggest eating five or six smaller meals a day rather than three larger ones. All of this is similar to the advice for the bulking phase of the bodybuilding diet.

Whatever approach you take, try to do even the littlest bit more than you did last workout. It won’t be possible every day, but over time, these small increases will add up. And don’t become discouraged if gains come slower as you get older; around age 30, you’re paddling against a slow tide of gradual muscle loss that makes gaining strength and muscle tougher than when you were younger.
Place your hands on the floor slightly wider than shoulder width apart and extend your legs behind you. Brace your core and lower your body until your chest is just above the floor. Take two seconds to lower down and two seconds to press back up. Remember to keep your back flat throughout the movement, your elbows close to the sides of your torso, and to fully extend your elbows at the top of the pushup.

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.