Doing push-ups or bench presses with dumbbells (heavy or barbells) is the best way to practice pectoralis major.
Doing sit-ups is simple and effective to practice abdominal muscles. You can also lie flat on the bed and touch your toes with both hands (lift your body). Do it slowly. If it is fast, there will be inertia, which will affect the effect. Be sure to do it to the end and do it in place.
Do sit-ups to effectively practice waist muscles, face the ground, lean out of the bed, half the body is still, take the waist as the axis, try to lift the upper body and repeat.
Doing bench presses with dumbbells (be sure to be heavy) or pull-ups on the horizontal bar are very good ways to practice latissimus dorsi.
The arm is mainly composed of forearm and biceps brachii, triceps brachii and deltoid muscle. Main pull of biceps brachii.