First an iguana is a wild animal and cannot be trained the same as say a dog. In some small ways their training is more like a cat. Most cats will do what you have trained them when they feel like it not when you want them to. An iguana is a lot the same. You may never be able to train him/her to sit still when you want it to even if it is calm to handle and care for eventually and under some circumstances you may not even be able to get the iguana tamed as they are "wild". As far as the lashing and biting when you reach in to take it out, I am assuming you have an aquarium? When you reach from above an iguana to pick it up it sees you as a predator. It thinks it is about to become your next meal and will defend itself to the best of its ability. Having it in a cage that opens from the side instead of the top would help a lot. Also you need to handle it daily building up to at least one hour a day. This can be at fifteen minute intervals, half hour intervals etc. If you can handle it longer than an hour a day that is also great. I don't know how much you have read on iguana care or know about iguanas so I will add a few more things. An iguana should be in a cage that is at least 1 1/2 -- 2 times it's total length tail and all. It also needs the right temperatures and UVB lights unless you live in a place it can get natural sunlight (not through a window) over 5-10 hours a week. It might be a good idea to pick up James Hatfields The Green Iguana Ultimate Owners Guide or Melissa Kaplans Iguanas for Dummies. Both are really good books and also have a lot of training/taming tips in them besides other good information!!
I hope you really care for your iguana and take the time to make sure you have everything it needs. I run an iguana rescue and have gotten in many iguanas from people who did not check what they were getting into first.
Anyway good luck!!
Stephanie