How should I choose my next step as a cook?
In my view this is pretty simple: make things you want to eat.

As long as you cast your net wide enough as you look for recipe ideas, there will always be new things that you'd love to eat and will learn something from making. And as long as you want to eat the food, you'll be motivated enough to actually follow through and do it.

Most of the time, this will mean making things where you're mostly comfortable with the recipe, but there are some new parts you haven't tried before. It might be new combinations of ingredients and flavors, which will broaden the creative side of your cooking. It might be new techniques, which will enable you to make more things in the future. To oversimplify, when you look at a recipe, if practically every step sounds new or difficult, maybe save it for later; if most of it gives you an "I can do this" feeling, go for it!

It's fine to take on bigger projects too, of course, as long as you go into it with the understanding that you might want to try parts of it by themselves first (or that things might fail the first time).

Either way, be sure to cast a wide net: skim cookbooks, read food blogs, browse recipe database sites or food photography sites, and so on. There's always a lot out there that you'll surely want to try and just don't know it yet.

But above all, just seek out things that look good to you (or your friends/family). The rest will follow.