Just go through all the games. Try each one and see what you're good at. That's what I did, and my game set can earn me a solid 20k in an hour and a half, though I only use it when I'm saving up for something.

One great game is hannah and the ice caves - you can find walkthroughs on neopets help sites. Once you unlock a stage, you can play it whenever you want, and the final level is extremely fast, and gets you enough points by itself to make HATIC a 3k per day game. The problem is, it could take a couple weeks to get far enough to unlock it - but hey, 3k per day for the rest of your life? It's worth the work.

Kass basher is also great. Unlock the bat, hit the kass as soon as it comes into range, hold the button as it goes up, release as it comes down, hold whenever it's touching the ground. Unbelievably fast 3k.

Other than that, it's discipline - don't spend anything except what you need to take care of your pets and maybe for dailies. To keep yourself from spending, withdraw your daily allowance for wheels or whatever, then make a bunch of 1np withdrawals until the bank refuses to give you any more NP for the day.