Making it work V/S Making it work right

Question

I am somehow a bit good at coding algorithms for small projects, but when it comes to make an attempt for some biggies, I make a total hodge-podge and marshmallows of my project's structure. I have studied a lot of books on software engineering and SDLCs where they say that becoming a developer is what every nook and crook can do, but the actual developer is the one who follows a systematic approach to the problem and solve it the way its meant to be.

My code works fine for such jumbled up projects, but it gets too difficult for maintenance and further upgrades.

So, I would like suggestions so as what should be the proper approach to planning the big moves