Midnight Spire and Pritt have some great advice, especially in regards to tutorials.
To add to that, I would recommend getting your basic game loop working before spending too much time with levels and assets. By "game loop" I mean all the logic from starting the game, playing a level and then failing or continuing to the next level, quit and restart options, etc. If you anticipate that your game will have a menu of some sort, do a very basic text-based menu first with only the most essential features (Start, Save, Load, Quit, etc).
Think of the "game loop" as the skeleton of the game.