First, confirm your ambition. There's at least a dozen of fangame attempts posted over the years, what makes you think yours will ever see the light of day?

Second, try some GameMaker tutorials and follow them step by step, it's usually a quicker way to learn than just action-reaction and see how it goes.

Third, communicate with fellow designers and share some work and ideas, the Official GameMaker Community would be a good start.

Fourth, SUCCESS! lol