1) Pay bills on time, only >30 day lates count for credit scoring, so if it's 20 days late, pay it now, don't wait.
2) Contact your lender
prior to the due date (or as soon as possible after) if you foresee a problem making a payment. They can work with you if you ask, but once it's late they
have to report it.
3) Prioritize the secured loans (mortgage, car etc), lates are taken more seriously on those than on revolving credit.
4) Have about 3 open (even if 0-balance) tradelines. No open credit = BAD credit.
5) Do not carry a regular balance higher than about 20-30% of the limit on any credit card.
6) Old credit is generally better than new credit. If you are going to close accounts, if it makes financial sense keep the older ones open.
7) Minimize your applications for new credit. Rolling maxed balances from 0-interest to 0-interest cards is bad for your score. (new credit/high balance issues)
Pay collections and past dues promptly. If you can't fight it, pay it. Don't be passive aggressive.
9) Get documentation of all payoffs of debt balances and collections. If there's an error in updating the report we can still remove the debt from your ratios.
10) You can get a free report (not score, that's how the bureaus make their money and thus charge you for it) once a year from each of the Bureaus (Equifax, Experian, Transunion) at
www.annualcreditreport.com. That's the official .gov mandated "free credit" website. You don't have to get all at once, I get them staggered at 4 month intervals so I can see if anything has changed or popped up.