[Dex]

If you do this, do yourself a favor and put a polyurethane (not latex) condom on the strap-on before she uses it on you. Latex irritates some people, and if you are one of them, this will turn out to be a very unpleasant experience.

Take a [censored] first and use LOTS of water based lube. Relax.

Have her put it in (slowly!) and then remain still for a few minutes while you get used to it before she starts [censored] you. If she just starts pounding away, you'll just tighten up and it will probably hurt. This shouldn't hurt at all; if it does, you're either going too fast, not using enough lube, not relaxed enough, irritated by the latex because you didn't listen to my polyurethane condom suggestion, or something similar.

Have her go first. You may actually find it arousing and then you'll get to [censored] her. If you [censored] her first, finish, and then let her do it, it probably won't be arousing at all - just uncomfortable.