Just like
Robor and a few others have stated, get a good, widely known brand and go from there. Foreplay is your friend, without making this a
XXX thread, we'll just say that it helps later on.
Girls on the pill... Personally, unless I was actually
there watching her get the shot, I'd use a condom. Unless you're seriously into this girl, been together a long time, etc. 'Cause if she's fibbing or the effectiveness has gone done since the initial shot, then my little guys are swimming around just waiting to tag an egg. And I don't want that. Condoms help protect more against STDs as well. With the pill, you can catch some interesting things, keep that in mind too. You don't know who else she's been with.
"Oh, you're my first!" Ri-ight. Nice way to try and boost my ego, the rubber still goes on.

Either way, buy a pregnancy test for her about a month later ....
Have fun and play safe!