First and foremost - be safe. Do not cut too deep and always be "sterile".
As for the marks - I hope you find peace with them. I view my marks as part of who I am and I am NOT ashamed of them. I am dealing with my issues in the best way I can. And if people want to judge - then they are morons because the alternative is that I would be dead.
Add on this fact..... As a cutter, if you saw marks on a stranger - would you judge? Or would you feel some form of comraderie? I fell and instant connection with that person. I know they already understand some of my pain and I understand theirs. In fact, I find marks totally sexy (but I am nuts).