How can I clean up my credit?

Clearing unfavorable credit history usually takes a few years and a good strategy. First review your credit report and clear any inaccurate information. Have the credit reporting companies remove any “paid in full” accounts. Pay off any accounts that are in arrears. Ask the creditor to remove all negative information from your credit file in exchange for a check for the outstanding balance.

Apply for and open new credit accounts only as needed.
Don't open accounts just to have a better credit mix - it probably won't raise your score. 

Have credit cards - but manage them responsibly.
In general, having credit cards and installment loans (and paying timely payments) will raise your score. Someone with no credit cards, for example, tends to be higher risk than someone who has managed credit cards responsibly. 

Note that closing an account doesn't make it go away.
A closed account will still show up on your credit report, and may be considered by the score. 

Re-establish your credit history if you have had problems.
Opening new accounts responsibly and paying them off on time will raise your score in the long term. 

If you have been managing credit for a short time, don't open a lot of new accounts too rapidly.
New accounts will lower your average account age, which will have a larger effect on your score if you don't have a lot of other credit information.

Keep balances low on credit cards and other "revolving credit".
High outstanding debt can affect a score. 

Pay off debt rather than moving it around.
The most effective way to improve your score in this area is by paying down your revolving credit. In fact, owing the same amount but having fewer open accounts may lower your score. 

Don't close unused credit cards as a short-term strategy to raise your score. 

Don't open a number of new credit cards that you don't need, just to increase your available credit. 
This approach could backfire and actually lower score.