Guys are stupid. The reason that's the stereotype is because it's true. All guys are stupid, and if you are in a relationship, at one stage or another, you are going to fuck up, and you are going to have to apologise to her. It's inevitable, so you may as well just get your head around it. But before you get too scared at having to apologise for something you haven't done yet, this is a handy guide to help you fix things with her, depending on how bad the thing is that you did.
Not That Bad
Examples: Calling her favourite TV show stupid, looking bored while shopping for dresses
Solution: A heartfelt apology
Examples: Not noticing her new haircut, Forgetting to text her back
Solution: Her favourite bar of chocolate
Examples: Drunk dialling her at 4am when she has work in the morning,
Examples: Saying one of her friends is attractive...
Solution: Flowers and pizza
Examples: Forgetting her birthday/ your anniversary/Valentine's Day etc.
Solution: one or more romantic meals, depending on how important the day was that you forgot.
Example: If you don't know what you did, how the hell do you expect me to know?
Solution: GIVE HER SPACE
Examples: Run over her dog,
Solution: All of the above... and Diamonds...