Start doing sit ups and push-ups each day.
They don’t take any equipment, and you can set reasonable goals for yourself.
Start off with 10 of each once per day, then move to 10 each twice per day, then 15 each twice per day, then 25 at once, 30 at once, etc.
The big thing is staying consistent.
Also - make sure your diet is (at least kind of) clean.