Great tips Oz. (Being a member of the Local Starwars Fanclub, I will be at the first viewing here in Antwerp, surrounded by Chewys, Darth Vaders, Emperors, Darth Mauls and hopefully an Amidala who will look into my eyes to see her own beauty reflected).
My tip, the first that comes to mind: sometimes you need the rectangular or other selection tools, like for example for cropping. And often your selection doesn't start exactly where you want it to. But if you drag while holding down the space-bar, you can move your selection without changing its size. Let go of the spacecake err -bar and you can continue drawing your selection.
Another selection tip I use all the time because I still haven't figured out how to get my circle selection just where I want to first time.........
circle selection tool - try to select as close as I need or want to [innocent] then use the arrow keys to move the selection where it is meant to be[excited]
Try creating your marquee type selections from the center outward... it's a bit easier to get 'em close then -- but almost everyone has to move a selection after creating it... that's not just you. [oops]
Holding Alt (MAC: Option) while dragging out the selection, does this function. Adding the Shift key to that keeps the selection proportionate as well as starting it from the center outward.