There are a few ways to get hemorrhoids.
1. You're preggers.
This is due to a) the vein around the anus being constricted by the weight of the kid (and thus, varicosities on that), and b) your liver working to clear up the blood of 2 (and thus the blood in that vein is very very thick: more varicosities).
2. You have one or the other food sensitivity.
This causes portal vein congestion, which leads to very thick blood in the vein around the anus, and thus varicosities there.
3. You're a bicyclist.
Boy, do you ever have hemorrhoids... because the blood just doesn't circulate, in that same vein. Varicosities again.
4. You're a coach potato.
Your colon walls are rather loose, and if you strain when going potty you're going to push some of that out. Push it back in, do Kegels (a bit further back than usual), and go for a walk now and then - a bit longer than between fridge and sofa, please. You can do astringent herbs, if you so like, but it's likely that they won't do all that much for you.
5. You live for sports.
When somebody asks you how many pushups you did this morning, you ask "left or right handed?" ... all your muscles are tight, including those around the colon. Relax a bit, and do relaxing and soothing herbs as well.
For the varicosities folks: lymphatics may help some. Going for a 30 minute walk 2-3 times a week may help some. Doing vein herbs (Crataegus, garlic etc.) may help some. Hemorrhoid or varicosity creams (like Aesculus, or pretty much any astringent such as Hamamelis) may help some.
But if you have a surefire help for the varicosities of pregnant ladies, do let me know about it, too.