Lenders like pristine credit reports. If you have a bunch of open credit card accounts that you never use (and who doesn't?), consider closing them. It will boost your credit score and make you a much more attractive borrower to a lender. Then, a month after you've closed your accounts, go over your credit report with a fine-tooth comb. It should read that the accounts were closed at your request. (You don't want lenders to think someone cut you off and that you're a bad credit risk.)
When refinancing, don't take the first offer that comes around. Instead you should actively compare both interest rates and lenders.
Ask for more than just rates. Bad loan officers will tell you anything to keep you on the phone -- then change the details to suit them later. Instead, make them get real with you! Ask how long they've been in the industry. Probe them about their experience in the industry. Also, ask what their opinion is on the current market and where it's going.
If there is a big difference between the initial interest rate and the APR listed in the ad, it may mean that there are high fees associated with the loan.