Personally I would start off by making a game design. Plan out what features your game will have.
Then create a prototype of the game design. Create some levels by hand and test to see if the game is "fun'.
When building the prototype build it up gradually. If you are making an iPhone game then the first task might be to draw a simple sprite to the screen....
After you have a working prototype and you are happy with the mechanics, then you have the option of modifying it to add randomly generated levels or starting "over" and designing the same game to use randomly generated levels.
I don't think you should work on random levels until you are fairly confident that you have the core game mechanics worked out.