The best way to train using pushups is to execute multiple sets of increasing repetitions using proper pushup form to avoid injury. Incorporating pushups as part of a total body routine is the best practice.
To complete a correct single pushup, assume a plank position, arms straight with hands shoulder-width apart on the floor slightly below the plane of your shoulders. Keep your neck, back and hips straight, feet hip-distance apart. Lower your body on a two-second count until your chest is about 1 or 2 inches from the floor. Elbows should not go below a 90 degree angle. To complete a single pushup, raise the body back up on a one-second count until the arms are straight again. Perform several repetitions with 30- to 60-second breaks between sets. Avoid curvature in spine while executing pushups.
If you are unable to complete pushups using good form with feet on the floor, modify by placing knees on the floor while still maintaining a straight back with arms in shoulder-width-apart position. It is better to modify for form or complete fewer exercises with correct form than to perform multiple exercises with incorrect posture. Pushups improve strength and muscle tone in upper arms, chest and core. Pushups are most effective when used as part of a total body workout rather than in isolation.