Mistake #3: Not lifting heavy enough
Keep in mind that “heavy enough” is relative. If you are new to strength training, using your bodyweight is usually plenty “heavy” in the beginning, and as you get stronger you can start adding external load to your training program.
You may start with Bodyweight Squats and over time progress to Goblet Squats, and then Barbell Front Squats and Barbell Back Squats.
You simply need to make sure that you’re always challenging yourself so that your body has to constantly adapt to keep up with the increasing demands you’re placing on it.
This is how you make progress in strength, performance, and body composition. There are many ways to progress exercises beyond just adding weight.