I am not really sure how experianced you are but this is one way:
- I would start by getting an image on the screen. Then moving it arround. Next get some enemies in. Get some basic collision in. and so on.
Ie build the game in small concrete steps.
Later as things work, some refactoring may be needed but at least the game works. Much better than being stuck in design stage and pre-mature optimisation with nothing to show.
Here is a really infomative guide about different ways to implement a 2D platformer: http://higherorderfun.com/blog/2012/05/20/the-guide-to-implementing-2d-platformers/
Also there is the lazyfoo tutorials which can help if you are wondering how to do something in SDL. here is the link: http://lazyfoo.net/SDL_tutorials/index.php