Depends how far you are into the project already ;-)
Basically I make a big overview listing the screens I'll need then the basic gameplay elements etc.
I always start on the game first and do the other screens later (because you might find that your game is rubbish after making it).
Anyway, pick an item from your overview list then plan it in more detail, and the code it. Keep a note of any ideas you get for improvements and log them to do later, not right now or you'll get distracted. Once that item is complete, tidy up any related loose ends and move onto the next overview item. Rinse and Repeat.
That's what I do anyway.
Basically I make a big overview listing the screens I'll need then the basic gameplay elements etc.
I always start on the game first and do the other screens later (because you might find that your game is rubbish after making it).
Anyway, pick an item from your overview list then plan it in more detail, and the code it. Keep a note of any ideas you get for improvements and log them to do later, not right now or you'll get distracted. Once that item is complete, tidy up any related loose ends and move onto the next overview item. Rinse and Repeat.
That's what I do anyway.