If it comes to it and bub comes early and you have to push (they will come when they want i suppose), try doing it in an upright and leaning forward position, it is the most natural position to give birth in and can minimise tearing. If they try to make you lie on your back on the bed like some hospitals do, this is only for their convenience and tell them where to go.

I agree that tearing in an earlier labour is not an indication that you will again, my sis had a 6lb baby and got 3rd degree tears with her first and had over a 9lb baby with her second and not a single stitch, she gave birth to her standing.

Good luck with everything