play the vanilla version of the game, see what's missing out or makes the game hollow for you (e.g. not that much variety, missing features, ...), then you can come up with a mod idea that can change it/make it better. alternatively, determine what you suck at in MC, and make a mod that adds features that'll make it easier, just don't make it overpowered
make an AI on a website that gives you ideas lol
search it up it is simple to make small mods
play the vanilla version of the game, see what's missing out or makes the game hollow for you (e.g. not that much variety, missing features, ...), then you can come up with a mod idea that can change it/make it better. alternatively, determine what you suck at in MC, and make a mod that adds features that'll make it easier, just don't make it overpowered