Lisa,
A few pointers that tend to cause new users the most problems:
1) Give you snipes 8 to 10 seconds lead time. Lots of users are happy with 5, but if you're sniping something very important, make it 8 or more. Ebay slows up at different times. AS tries to compensate, but they can't always make the correct adjustment. Help them and yourself with longer lead times. That's why Steve said, "it's not who gets in the last bid, it's who gets in the highest bid that wins."
2) Turn off your "Instamail" option. It's on your "Modify Account" under "My Snipes" page.
3) Be careful of bid groups. They don't clear themselves after you use them. So if you add more snipes, they won't get placed. Best to delete the bid group folder after you've used it.
4) After you use up your free snipes, consider giving AS your credit card #. You can pay them with Paypal, but it's a manual process to apply the credit to your account, and it takes 4 or 5 days. And if you do use Paypal, remember there's a charge AS has to pay. So paying AS $.25 will leave them with no money.
5) If you place a manual bid, and don't cancel your AS snipe, AS will still try to place the snipe. Even if AS doesn't get the bid in, they still had to use their resources, so AS will charge you.
6) You have to cancel a snipe at least 2 minutes before the time the snipe is to be placed.
7) And, regardless of what anyone says, Steve is not on AS' payroll.
I'm sure there's more, and hopefully those tips that I missed will be mentioned by others.