There are many ways to get wood flat, straight and square - but for this instructable I'm going to stick to using the power jointer, power planer and table saw. I'm fortunate to have access to all these tools at Techshop, San Francisco, so I take full advantage of them. I'll start with an overview of the general process of jointing and planing, then I'll show how to use the jointer and planer to fix specific defects that commonly occur in rough cut wood.
For those without the money to buy all these tools, or the shop space to house them, there are other ways. My favorite woodworking podcaster, The Wood Whisperer, has a great episode about this topic - Episode #6 - The Jointer's Jumpin. He not only talks about the method I will show here, but also demonstrates how to use some other power-tools, including handheld routers, router tables, and the table saws by themselves. You can also use hand planes to clean up wood very effectively, but I'm not yet familiar enough with that technique to write about it.
As always, I'm still a relative newcomer to woodworking - if anyone has any corrections or additional information, please share it in the comments. Just keep the criticism constructive.