Great question. The answer is not so easy though. I obviously recommend The Quest Podcast for some info (you can find it here on the RPGSC.org), but that's self indulgent.
There are a number of great resources out there though. I recommend watching the GM Advise by Matt Mercer videos on Geek and Sundry: http://geekandsundry.com/tag/matt-mercer-gm-tips/
Matt Colvilles YouTube Series, "Running the Game": https://www.youtube.com/watch?v=e-YZvLUXcR8&list=PLlUk42GiU2guNzWBzxn7hs8MaV7ELLCP_
Read the GM sections of some great RPG books, like Legend of the Five Rings 4th Edition, D&D 5th Edition, 7th Sea 1st and Second Edition, and the World/Chronicles of Darkness books if you can borrow them.
There are a number of blogs as well, but I won't start listing those here.
I would also suggest going to local conventions and attending panels, talking to players and GM's, and watching/playing in a variety of games if you can. It can really help you learn what style of play you are most drawn too.
Once you have the basics you can start on more advanced GMing stuff like these books:
John Wick's Play Dirty Books: http://www.drivethrurpg.com/browse.php?keywords=John+Wick%27s+DIrty+Tricks&x=0&y=0&author=&artist=&pfrom=&pto=
Kobal Press Guide to WordlBuilding: http://www.drivethrurpg.com/product/109707/KOBOLD-Guide-to-Worldbuilding?term=kobold+World&test_epoch=0
Hope that helps!
"Time wounds all heels" ~ John Lennon