Hey guys, new to the site and basically new at guitar. I've messed around before but now I want to take my playing to something more substantial. Here's the rub:

I've been working my way through the beginner's guide and have had little problem up till now. I am unable to form an F-major chord. My middle finger just can't seem to not interfere with the B and D strings when it's supposed to only work on the G. I'm able to form the rest of the chord but I cannot for the life of me get it.

Is there a trick with thumb-positioning that makes your hand more easily contorted to that form? Is there some trick I should know?

Thanks in advance,
Nate