A few suggestions:

1. Try increasing harder hacks to progress your skills. Or try the same hack on multiple games to better understand things on the concept or big picture level. If you take several games and do the same font hack for example, you're likely to be exposed to many ways of doing the same things or new tricks or hardware use you didn't know about. However, the differences will be small enough that it is within your grasp to figure out without being overwhelming.

2. Try doing some homebrew coding. There's no better way to really learn the hardware platform and assembly than doing it yourself from scratch. Try to get a single screen up and running. It will go a long, long ways to understand how games work and more advanced hacks.

3. Read additional hardware documentation. 50% of doing advanced hacks is better understanding of hardware so you understand what the code is really doing and what your options are of making advanced changes.

4. Help someone else out on a problem or project of theirs. Nothing reinforces your own knowledge better than helping someone else.

5. Experience. Just keep doing it. The more you do it, the more you're exposed to, and the more you challenge yourself, the more you will learn and the more proficient of a hacker you'll become.