The next element to create are the enemies. They should match the style of the main character.
In this game (the super crate boy style platformer I am aiming for) they should be clearly identifiable as targets and stand out well enough.
A common problem with a lot of 'coder art' I have seen is the inconsistency in style. This becomes even more visible when the art for the game is 'collected' from across the internet. It's perfectly alright for game engine testing to use whatever is available as long as you remember to bring it inline and replace the bits that are not matching before publishing the game.
Exporting those three designs to our player size of 48x48 pixels looks like this:
The animations for our player and the enemies will be covered a little later. Next up are the platforms and the background for the game. That way all the core elements are in place and you can see how they work together. That way you avoid losing yourself in details and eventually having to redo a lot of the work because it's not matching the rest.