Once you have graduated from Wall and Bar or Staircase pushups, you can try the Pad pushup. The advantage of the Pad pushup is that you are on the floor in the proper position for a full floor pushup.
Place a pad or yoga block under your legs while maintaining a good plank position. Start by placing the pad or block under your thighs and perform a pushup. Move the pad or block lower on your legs toward your ankles as your strength increases. Continue moving the pad or block lower over time until you are able to perform a full pushup without any assistance.
Work with a personal trainer to help you with proper technique.