simply select a profile of a girl you are attracted to, and write down 5 to 10 openers that come to mind - Just write them down - No shame!
Don't send them, yet!
Once they are written, give them a mark 0% - 100%
select the best - pimp it a bit - send it!
You have to start by writing, by moving, even if for you a message or line might sounds stupid at first. That's the only way to learn ;)
I'll show you what to do next