In my career as a mortgage broker, I have dealt with thousands of clients. I would say that one of the most misunderstood areas of personal finance and qualifying for a mortgage is credit.
First Foundation has an excellent Mortgage Glossary and has several entries that deal directly with credit scores and credit reports, so I will point you there to set the groundwork. I would like to go in depth with one particular issue or question that seems to come up a lot, typically with First Time Homebuyers. "Does pulling my credit score hurt me"? I have recorded a sound bite discussing this very question, check it out below.
"Credit Inquiries will not make Good Credit bad, However it can make Bad Credit worse"