kevodoom

My recommendation for this would be twofold: Grab an Unreal 4 subscription and burrow through the ever-increasing collection of tutorials there. You'll learn the nuts and bolts of level development using the same tool the professionals use. To develop your design skills, there are three books I'd recommend you read, in this order: Raph Koster's A Theory of Fun, Jesse Schell's The Art of Game Design, and Katie Salen and Eric Zimmerman's Rules of Play.

Following these two tracks of learning the practical elements of game development along with the theory of why game design works the way it does will get you started on a good footing.

(He's talking about Hearts, Clubs, Diamonds, Spades: Players who Suit MUDs, by Richard Bartle. This is one of the foundational essays of current game design thinking. Absolutely worth reading.)