Do not be eager to sleep with her. Better yet, pass up your first chance to sleep with her. If you do this she will know that you respect her and that you are not just looking for a good lay; women worry about being used.
Absolutely avoid the relationship to get based on sex. We all know sex is a great thing, but in a serious relationship that cannot hold. If both of you are freaky that is fantastic, but on the reverse side, you might have to make sure your mentally attracted to each other as well. Do fun things that do not end with sex at the end of the day.
Do not start problems with her friends. I know it is rough sometimes, but you have to do it. If her friends seem to upset you every time you are around them then either change their point of view on you, or simply do not be around them so much. Some women rely on their friends support (I know it is incredibly sad). If you start by having trouble with her friends, most of the time it is not that difficult to remedy the situation. Try to be nice, but not so nice to the point where your girlfriend will think you’re too much of a pussy.
Avoid being fake. Do not pretend to be someone you aren’t. Just be yourself, if there is a small change to make; for example, being more relaxed, or calm, then you will be able to slowly change into the habit of dealing with situations differently, but in no way should you try to be something you are not. Later on in the relationship your true self might come out and ruin your relationship. If she does not like you for who you are she does not deserve you.
In no way let her lose trust in you. If she loses trust in you it takes forever and a lifetime to get her to trust you again. Losing trust in your partner or vise-a-versa will make the relationship much more difficult so avoid losing her trust. Try not to lie to her, especially about big things. Some white lies are okay…if she never finds out, and if it isn’t a big deal; after all, ignorance is bliss. Do not get into a habit of lying or not telling her things; she will mistrust you. Just let her be able to trust you and things will be great.