If we’re going to talk about pushups only… I see this as a few different problems.
- you need to be able to do a pushup
There’s a few things you can do, and you should probably do a bit of all of them.
First idea: Work on doing a pushup with your feet on the ground, but your arms raised off the ground: so put your hands on a coffee table, on a couch, whatever. You want to start with something you can do a few pushups against, and over time, you want to get closer and closer to the ground. Today you might be able to do 5 pushups with your hands on a countertop. Next week, you might be able to do 5 pushups with your hands on the ends of a couch. The following week, on the seat of the couch. Eventually, work your way down to the floor.
Second idea: Work on holding a good solid plank position. This is pretty much just the top of the pushup position. You should be able to have your arms straight, and keep your body straight for a minute or more.
Third idea: once you can hold the plank, is to work on slowly lowering yourself to the ground. Keep your back and legs straight, but see how far down you can lower yourself before your arms give out. Repeat this for a few times.
- you need to be able to do several pushups
With this, give yourself a target number, so 20 pushups. Your goal is to get 20 pushups over the course of the day. You can use as long of breaks between them as you need, but just get them all in by the end of the day.
Do this with whatever type of pushup you can do right now. If you can do knee pushups, do those. If you can do pushups against the edge of a couch, do those.
I’d work on getting up to doing 50, every other day.
- you need to be able to do several pushups in a single set
This sort of comes along with the last one. So let’s say you’re now able to get 20 pushups through the day. You do two here, three there, but eventually hit 20.
Now you try to get more pushups in each chunk. So instead of doing 2 pushups at a time, 10 times a day, work to doing 3 pushups, 7 times a day. Then work up to doing 4 pushups at a time. Then 5. And eventually you can work up to doing all 20 at once.
Both of the last two can be done with whatever kind of pushup you can do… so just find some variation that you’re able to do right now and start working on improving your numbers. Eventually you can work up to doing “real” pushups like that.