Here's some basic tips for a new GM:
Try to get 3-4 players (not too many, not too few)
Try to get an "experienced" player to help the newbie, so you don't have to.
If you're all newbies, learn the basics (ala D&D3.5-1.5)
Know how to roll an attack (1d20 + level bonus + STR bonus) > AC = hit
Know how to roll a skill check (1d20 + ranks + stat bonus > DC = success
Use DC15 and DC20 for basic skill checks (DC15 = challenging, DC20=hard)
Get those basics down, before you worry about how specific feats work, and how to use Attacks of Opportunity (in fact, first fights, ignore them).
Tell the players what rules your using (and ignoring for teaching purposes)
Avoid Dream Sequences, they're a bit cliche for "I didn't mean to kill your PC"
Avoid capturing the party (if you capture them, they'll want to escape. It's harder to manage that if you hadn't planned it all)
Never assume you will be successful in having something happen to the party aka RailRoading the party, ie. The duke will capture the PCs here, and take away all their armor and make them go through my dungeon. First off, the party may surprise you and never get captured. Secondly, if you force them by making sure the party always loses, they will not like the game.
Avoid sexual references (at least until you know everyone very well). That means don't rape the PCs, don't strip them naked, don't even play out pick-up lines. This can get out of hand, and easily offend someone's PC.
One new GM I played under made the mistake of forcing a party capture and then stripping all the PCs naked (2 female players) and taking all their stuff (in the first game) because it was the "smart" thing for the guard to do (can't hide anything). This breaks both the don't railroad, and don't mention sex rules, and it really bothered the players. Pretend you're filming an action drama for the 7PM time slot. This gives you a sense of what types of things to have happen in the game.
Early off, keep the plots simple:
1. somebody pays or asks the party to go somewhere and do SOMETHING
SOMETHING = get item, rescue person, kill critter
2. party journeys to place (through town, across land, etc)
3. Party searches place (ie. dungeon, sewer, castle, house) for SOMETHING
4. Party does what is needed to "do SOMETHING"
5. party returns to collect reward
Write up a bunch of these at once, and offer the hooks, run the one that the players bite on. This also gives them something to pursue (after we rescue the princess, let's go fetch that Fungus for that mage")
Just a few tips,
Janx