Push ups are great full body move. They require not only upper body strength from chest and shoulders but also the core, glutes and legs for stabilization and good form throughout the move. So many people end up doing push ups wrong thus putting them at risk for injury. 
Here are two modifications that will help you gain the strength needed for regular push ups.

Move 1: one leg push up

Start with knees on the floor but as you lower yourself straighten one leg.  This move helps strengthen your core, helps prevent low back sag and replicates the form you’ll want to have during a regular push up.

Move 2: power up push up

This move is a step closer to a regular push up.  It allows you to practice lowering yourself with no assistance but placing knees on for at bottom of move to press up, power up, through chest. Again this move helps with proper form and technique of av regular push up.

Try incorporating these moves 3-4 times a week and I promise you’ll gain the strength needed to do a regular push up with good form and technique!