Here is what I have learned from the research I have done after experiencing this myself. After an ectopic pregnancy, you have a 50% chance of a subsequent pregnancy. You have a 15% chance of that being another ectopic pregnancy. There is really no way to prevent an ectopic pregnancy. The only thing you can really do is try and hope for the best. Just be sure to get into your doctor as soon as you see a positive home pregnancy test result to check for an ectopic. Your doctor will probably want to monitor your hcg levels. Once your hcg levels have reached 15,000, he will then probably perform an ultrasound because by then there should be a visible fetus in your uterus (if it's not ectopic). If you cannot seem to get pregnant naturally, then in-vitro is your next option (costly but worth the try). I wish you all the luck in the world with this. I just had an ectopic removed yesterday (my first pregnancy) and had my entire left tube removed as well. It's been the worst emotional pain I have ever had to deal with and it helps to be informed and take an active part in your fate instead of just waiting and wondering (for me at least). Good luck again and I wish you nothing but the absolute best.
There is nothing I know of that can prevent ectopic pregnancy. It is up to the fertilized embryo on where they implant. Good luck!