1) Pay your bills on time and pay off any prior dues that you have.
2) Ensure that there are no negative status reporting from old loans that you have, and that all previously closed loans are reported appropriately.
3) Ensure optimum credit utlization of your credit cards - do not over-spend or not use your credit cards at all.
4) Have good mix of both secured (home loan, vehicle loan, etc.) and unsecured (credit card, personal loan, etc.) credit exposure.
5) If you have an excess of cards and you need to close some, close the newer cards as compared to the old ones. Keeping older credit cards signifies that you have managed credit for a longer period of time and tends to have a more positive influence on your credit worthiness.
6) Try not to change your employer or place of residence often."