Understand that girls are built differently, and they are absolutely not interested in fast cars and monster trucks and the like. This is one of the primary facts about girls every guy should know.
Girls need to know a guy cares about them when they are in a relationship, so before you start to wonder why she is acting all insecure and upset, ask yourself when you last told her you loved her. Guys hate emotional stuff, but girls thrive on it. This is especially true when it comes to verbal expressions of love—girls like you to say: “I love you” as often as possible, and no, saying it with flowers is not the same. Saying it at the point of orgasm also doesn’t count.
Girls do not appreciate it when you flirt with their mates. Although you might think her mate is slightly better looking and has a great pair of assets, keep your eyes to yourself and save those fantasies for when your girlfriend is not in the same room. Even if you think your thoughts are private, trust me, she can read your mind and she can tell when you are drooling.
Girls in love will laugh at all of your crummy jokes, even when they are not funny. To her, everything you say will be amusing and witty, despite the fact nobody else thinks so. Make the most of this blissful period—it will not last forever and before you know it, your rubbish jokes will be met with a stony silence and a look that would have Attila the Hun quivering in his boots.
Get used to apologizing, because whether you did something wrong or not, you will always be the one apologizing. Girls love that, and they cannot stand guys who do not know how to apologize. Practice your apologies in front of the mirror everyday, and you will thank me later.