I can tell you from personal experience that one of the fastest ways to boost your credit score is to pay down your debt. I have seen people with 700+ credit scores get turned down for loans because they are so high in personal debt. Here's is what my mortgage guy had me do when I bought my house and it worked. I raised my score almost 20 points in 2 months, but I needed his help.
1.) Every credit card or loan that is over 50% of your limit is VERY hurtful to your score. For instance, if your limit is $1,000 and you balance is $501.00 or over you get dinged big time for that. I paid down a few credit cards that were above 50% of my limit and it helped a lot.
2.) Do NOT close any credit accounts no matter what. This hurts your debt to credit ratio as well and can make your debt look even worse believe it or not.
3.) Check your credit report and contact the company's if there is any false or out dated info there. If it turns out to be true they must
remove it by law which will also raise your score.
4.) Do not charge anything new or open any new accounts until your refi is over. That will hurt you big time. Every time you get an inquiry on your credit it lowers your credit score as well. even if it's for a good reason.
Every time I made a positive change to my credit score my mortgage guy would fax the credit bureaus and ask them to bring my credit up to date. If you wait for them to do it, it could take 30+ days. if it's a positive change and a mortgage guy is contacting them they are much more likely to make the change more quickly.
A good mortgage guy can help you with this easily. Just be sure you find a GOOD one and not one who will rip you off in the end. They are on your side because they get a commission if they get the loan so a good one will go out of his way to help you with your credit in any way possible. Ask them for help. you'll be surprised at what they can do!