First of all, I am a beginner myself, that's why I can give you some good tips for the beginning.
In the beginning, you should first try modding simple .dll or .so games.
What that mean?
For example, do not try Netmarble games or games like Maze Shadow of Light.
These types of games or these companies protect their games via very strong anticheat software.
If you're trying to mod this kind of games right from the start, you'll quickly lose the pleasure of modding, as you will not feel any success.
Especially for games like Maze the Xigncode are protected, or games with an Apk Hash Protection.
This kind of protection is a step harder than a simple Google Signature Check.
Start with simple games and work your way up to the tough ones.
Watch video tutorials on Youtube and try modding these games (these are usually very easy to mod)
Sure, you can jump straight into the extremely heavy games, but unless you're a genius, you'll feel little to no luck
And important : find your own way. Don't copy ( leech ) other mods. That brings you nothing, only hate. I mean, sure, you can hack something because you copy the code or instructions from someone else, but you don't understand what the code does. Modding isn't only copy & paste codes, modding is to understand how this games and how the code works.