How can I please my girlfriend?

[(;]

"*Girlfriend's name here* is so bomb <3"
Haha, something like that.
Or you could post something that only the both of you know (e.g. an inside joke like Smiley said) or a funny/romantic/pleasant experience that you two shared. That would make her happy to see that you remembered it.

If she's the kind of girl that DOES like to boast and let other people know about your relationship, then if you want to please her, i think you should post a status about your relationship even if you don't like doing it.
Example: "I love my girlfriend <3 *insert the date you guys started dating here*" or "I'm so happy she's mine."
A lot of people do that and i think it would make your girlfriend happy. (: