Timing is critical with this next exercise. How you 1) apply for new credit, 2) close credit, and 3) ask for credit increases will affect your score. All these activities done separately, scattered throughout the year, have a more sustained lowering affect on your score than does having it all done at once. However, you may want to do these three things every year.  

     Once a year ask all your creditors at the same time for a credit limit increase. Call them one right after the other one day. I suggest timing all your purchases that will require a loan for that day as well. During this time you may apply for additional cards / accounts / loans if you need to / want to (as long as you have a valid credit building reason). Get rid of the cards and accounts you don't want anymore or are not working for you the way they should. Open new accounts that will reward you somehow throughout the year or give you better interest terms.

     This is a good time to check your credit report again. Once a year the credit bureaus are required to provide you with a free copy of your report.

     Personally, I don't think it is fair, but inquires (other than yours) into your credit make your credit score go down temporarily. If you have inquires several times a year you have a regular stream of input into your credit that is keeping the score lower than it needs to be. Get all inquires done in one shot. Take the hit only one time.

     Real Life Story: When I was in the process of rebuilding my credit I was trying to open new accounts one at a time and received many "nothing we can do for you" letters. Then I changed my tactics. I had decided on three credit accounts that made sense for me and two accounts that I wanted to close. When the day arrived, according to my financial plan, to apply for the new accounts I applied for each one of them online. That allowed me to control the timing of when the companies would look at my credit - all in the same hour. Within that hour all three had been approved. I now went and called the other two accounts and cancelled them over the phone. By the time all this information was reported to the credit bureaus I had my new accounts.

     2-3 months prior to applying for new credit or credit increases make sure there are no balances on any of your accounts. When the creditors look at your credit report they will find that you now have a history of responsibly using your available credit and don't owe any money.