Rule #1: Know your bottom price BEFORE you go in and don't move off that number no matter what. If they won't meet your price, walk. Don't get swayed into making payments higher than you can afford, you'll regret it and you'll not enjoy your car (as much).
Ask about rebates, especially on 2012's. Look at neighboring dealers to see what they offer and go with the lowest price. Also, confer with your local Credit Union to see about their financing. Their rates are usually lower than the dealers and those "special rates" the dealers offer aren't always your best bet, compare numbers over the entire contract length, not just monthly.
Good luck though, your first car purchase will be memorable and you'll really enjoy your Focus. Keep us posted.
2012 Silver Ingot Titanium Hatchback
Premium Package, Sport Handling Package 18" wheels
MFT w/Navigation, Parking Assist, Rain-sensing wipers, leather seats