1. Probably the most obvious and also the most important is always pay on time. Keep in mind that once you are more than 30 days late on a credit account, there will be a derogatory on the credit report.
2. Have a variety of credit types extended to you. For example, credit cards, car loan, student loan, mortgage loan, etc. These are all different types of loans as seen by the credit bureau.
5. There is a common misconception that paying off collection accounts will help your score, however this is not necessarily true. A collection will show "paid collection" and will still have a negative effect on the credit score. You will get more bang for your buck by saving or paying down revolving balances.
When working with my clients, I help them prepare for the buying process. Wheather just getting starting to build credit or many derogatory items which need attention, I will help with the process. I understand that it takes sometimes over a year to buy a house and will help each step of the way.