Whether it's time, reps, or sets, keep a count or tally. It's how I got to 1000 pushups a day or literally hundreds of pullups. Not all at once, but in sets with a minute or two in between. I mark it on paper. Then week by week I want to increase the tally marks. Before I knew it, I saw how close I was to 1000 pushups (sets of 20-30 with 1 minute break) that I just decided to go for it. I made clear, well-defined goals for myself. Of course I wasn't able to start with 20/set. Maybe 10, then go up from there. My initial motivation was starting a career in law enforcement. I wanted to be able to pass the physicals without gassing myself out. I looked up the requirements and built myself up to that. Then beyond. Pick a standard, like Marine PFT or CFT and train to it.