I know I'm not a girl, but there's really no "average girl" on this. There's great ways to not start sex. But it depends on the situation. Do something that implies that you want to do it, and let it flow organically. Don't think about it so intricately.
I'm not a girl either but here's what I've learnt.
Sex should be spontaneous; if you plan it it ruins everything, really.
But when you are /starting/, start with foreplay. Tease eachother, stimulate the female with 'hand' and 'head' and have her return the favour.
Ask her what she wants, also, so you don't do something that she doesn't like/feel right about.
Then when the time comes for penetration, let her be an active part in it; let her play with herself or you as you enter, or let her 'guide you in'.
Make it last as long as possible too; 5 - 10 minutes might be ok for you as a guy but not so much for the girl; if you can try and 'last' for 45 - 60 or so minutes, that's good for both of you.
The more you do 'it' the better your stamina will be - the longer you will last - apparently my gf knew/knows someone who can last 5 hours straight . Myself, I can last 60 - 90 minutes or so. It's down to you as the person but longer (time) is better.
Stuff like this should really come naturally. One "step" should progress to the next without having to think 'what should I do next' - if it doesn't, to me, that would show that the comfort level between you and your partner has not developed to that point yet, and you should slow down.