Hmmmm I think the first stepping stone should be the foundation of your game: what's the main thing that people will do in it. Since you want it basic, let's stick with what i believe the canvas for many indie, successful games -->Platforming-Puzzle I could also recommend giving it rogue style elements,to "up" it's replayability and keep people coming.
In order to make it more fun, I think you should achieve this through the vibes and style.
Some games that are fun and basic in my mind is Binding of Isaac,Slay the spire,Enter the gungeon,Hollow knight and A Hat in Time. Checking out other games and getting inspiration should be you go-to priority.Just see what you can do better.
P.S.I have an idea for a game but i don't think it is much basic and it's gonna be length-y.I am willing to share it with you if you want.DM if you do.
Since you're just starting I would say try and make something simple, so you can get the basics down. How the logic works, the best way to do and so on. So for that maybe a game like Pong or some simple plataformer.