Getting a card just for the miles?
 

I got an offer in the mail for the Citi AAdvantage World MasterCard which gives 12,500 miles and has no annual fee for a year. I know that cancelling a card is supposed to lower your credit score because your available credit is reduced, but wouldn't getting a new card increase your score? So if one were to get a new card, make a purchase, get the miles, and cancel less than a year later would the net credit score go down? Thanks for any help.

Pay your bills on time and you will have no problem. If you close a card be sure they note "at customer's request" on credit report. And don't forget to check your report often for errors or attempts to misuse your info.

Your net credit score will generally go down, since inquiries adversely affects them. However, as long as you don't have a lot of inquiries, then you should be fine. Just don't apply for a half dozen credit cards for the bonus miles or points and then cancel as many inquiries within a small timeframe will lower your credit score. Inquiries remain on your report for 2 years.