Other than the obvious (lots of water & fiber in your diet, not straining to go potty, sitz baths, keeping the area clean, using Tucks pads & Prep H), there isn't much you can do with a vaginal labor to prevent one from worsening if it's already there.
I've had one since the first trimester, but since I'm not really stopped up anymore, it's been kept at bay. This sounds so gross, but seriously--keep it clean with moist TP and in the shower gently wash the area since it can get infected/bleed.
I have no birthing experience with hems, but I'm just bringing Tucks and ice packs to the hospital for after labor. I hear a spray bottle helps, too, when things are really sore down there & you don't even want to wipe.
Muffin, 2010
Bubba, 2013
"You've probably heard the expression 'I believe in God, just not organized religion.' I don't think people would say that if the church truly lived like we are called to live. The expression would change to 'I can't deny what the church does, but I don't believe in their God.' At least then they'd address their rejection of God rather than use the church as a scapegoat." Francis Chan