IMO you shouldn't send her a friend request right away. For me, the best way to open is to send a message, but be careful, hot girls receive over 100 messages per day and 99% of those are super boring, such as "hi how are u", "wow ur hot" and so on. Make sure your messages stand out in her mailbox. I think it's OK to send a friend request after a few messages. Which openers to use - you can either make a comment about something on her profile info or to use a canned opener which you can send to numerous girls at a time. I hope I've helped you, good luck!
