step 1: figure out how much You can afford. AFFORD. Just because You can MAKE the payment does not mean that You can afford it.
There are a ton of financing options out there, talk to a few loan officers about their products to see what will best fit Your situation (5 yr occupancy? 40 yr occupancy? gonna die in that house?).
Once You have a strong idea about the financial terms… rate shop.
Ehh… cards can help & can hurt. You need to understand how it works before You start opening cards/accounts for the helluvit.
http://www.myfico.com/ <- FairIssac is the model that >80% of the financial institutions use. Read up. A mere 20 pt swing in Your score (at the time of application) can mean as much as 1.4% interest rate change.