I have found the most important thing to get right, even before anything else is the diet. For me, nothing else did much until this was taken care of and in fact if I had to do only ONE thing, that would be it.
Detox and health rely on the gut and liver, and if a person is suffering too much yeast overgrowth (candida), their immunity is down, etc, they will likely have problems with detoxing and be much more suseptible to damage/exposure during removal and have problem after with eliminating the poisons.
That is my experience with myself. A top dentist here in my country who has studied extensively (biologic), now refuses to remove amalgams from his patients until he has them pre-prepped beforehand and he now starts with the diet.
This diet is an antiyeast diet and usually improves the gut and liver. All sugar in all forms MUST be eliminated completely. Sugar, honey, fruit, milk (lactose), high carbs like potatoes (potatoe chips etc). Eliminate caffeine, cheese, high gluten grains or old world grass grains if a person needs to do more than just get rid of the gluten ones - wheat, rye, barley, oats, millet and rice.
Concentrate on consuming meats (chicken, beef, lamb, liver, turkey), eggs (free range), vegetables (stir fry, steam and/or raw), plain sugar free acidophilus yoghurt, raw nuts (almonds and brazil safest), herbal teas.
Also make sure you have enough essential fats in your diet like fish oil (mercury free), olive oil (in salads/cooking), butter, (cooking and spreads), flaxseed oil (teaspoon mixed in with yoghurt 2-3 times a day).
These are just suggestions, but the only thing that really helped me at all. Beyond that? The rest to me is just supplementary and an aid to this.
Supplements like selenium, vitamin C, vitamin E, zinc, Microhydrin (can help too apparently) seem to all be pretty good in a mercury toxic condition with support and protection and aid to detoxing, along with the proteins and fats in the diet.
Some people take products like algin or charcoal in an aid to help mop up any mercury or new mercury they might be exposed to (e.g. during procedure). It can be taken before the appointment and after. Best taken away from other supplements to avoid clashing or even absorbing nutrients. between meals might be wise.
The diet for me is the one though and takes a few weeks normally to notice a difference. Cheating on the diet is not wise, can lead to a relapse.
I hope this is somewhat helpful.
There is a list of dentists on this web link and you can click on whatever area is of interest to you. Make sure when you do click on an area, you scroll properly down the page because it can be a bit deceptive and seem to show only one dentist, when there maybe other beneath.
http://www.holisticdentalnetwork.com/directory.php#USA