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. 
The pyramid system of training was in vogue during those days. Bodybuilders using multiple sets per exercise would typically warm up with a light weight and gradually increase the resistance over the 4-5 sets so they were using their heaviest weights for the last sets. As mentioned above, the bodybuilders would start training faster while still using heavy weights as the contest got closer. This would increase the intensity of the workout while still using the same weights because of the decreased rest periods.
For every person who lifts weights these days, it seems there are two who have a podcast about it. There are more bodybuilding tips promising greater strength and muscle than ever before, and along with them a ton of confusion; one buffed-up Instagrammer says lifting heavy will get you swole, while a well-known fitness personality has claimed in recent years that two 30-minute workouts per week netted him 34 pounds of muscle in a month.