Begin to exercise slowly. As you perform gradually increase speed and do as many reps as you can. The number of times depends on the state of your health. Perform no more than 4-5 sets.
Do not forget to exercise regularly. Do not make long breaks, always try to increase the number of repetitions. Need to keep muscles toned, otherwise you will gradually regress, and the muscles will gradually weaken and deteriorate, because the body does not get enough load, and therefore it will have no incentive to maintain its shape.
The most important thing - to get lessons from joy and pleasure. Do sit-ups for their own development, rather than to someone to prove something. Do stretching exercises, different inclinations. Sit on the floor, slowly pull your socks without bending the knees, try to engage in this position as long as possible.
Squat with a barbell
If you're doing squats with weights and you have started "stagnation", try to add variety to your workout. In particular, make sure technique for exercise, maybe you have not noticed, they started to make mistakes.
Review your training program, pay attention to other exercises for legs and other muscle groups. Do not forget that the body - a whole, and if some major muscle group does not develop, it leads to stagnation in other parts of the body.
Do not turn the load on the legs more than one workout a week. Give a muscle relaxant. If you feel tired, then take a break from squats for about two weeks. Use ready-made training programs to professionals, work out with a trainer, so he helped you in the classroom. Reassess your diet, use of sports supplements, if you have plans to prepare for competitions. The higher the motivation, the more results you will achieve in a given period of time.