A technique from game development: grayboxing.

The most important thing is to find the fun and then nurture and grow it.

The fun emerges out of the fundamentals, not the aesthetics.

So you throw together a "gray box" prototype: where instead of finished assets, you have just gray boxes.

If it's fun with gray boxes, it will definitely be fun with real assets.

If you did real assets first, you'd waste a ton of time on a direction that might turn out to not ever be fun.

But you also might trick yourself into liking it even if the fundamentals aren't strong: "it's so pretty!"

Aesthetics can hide fundamentals.

So remove aesthetics to see the fundamentals at the beginning.

What things to graybox is a matter of judgment.

For example, if you're making a platformer with a new jump mechanic, you'll want to dial the jump mechanic in with very high fidelity to test it out–but the animations could all be grayboxed.

What parts to graybox are the parts you're confident, based on your experience, that you can later fill in in a sound and compelling way within the rest of the system.