One of the first things my mom and dad taught me about how toto build a puzzle was to separate the corners out of the whole puzzle. And since then it has been my first step and my tip for anyone that ask me for help.
Just few days ago, I found this cool article of 5 tips for doing your first puzzles. While reading this article I realize I do some of those 5 tips with out realizing I'm going them.
Here is the article: