I've made several trips in the last year and the advice above is very good. The way we do it is we bring 4 suitcases. The smaller fit inside the larger for the return trip. We remove tags and wash as stated above. We usually have some obvious new items that are in their package and we declare them. We have found the customs people to be very polite and fair.
Now as far as how much you are going to pay. I think it depends on who the customs person is and what mood he is in. I have never been able to figure it out. I usually tell them that it is small household items. They always look at everything but I've never been questioned yet. Sometimes I think I'm a little to honest but what the hell we are not talking about that much money. If I had to guess I would say about 33% of what you declare.
Be sure to have cash and some small bills because that has been an issue with people in front of me on two occasions trying to make change. Once you bring in one load it gets to be old hat and nothing to really worry about. What Gwen said about lamps was absolutely true with us. We had quite a time to find any that my wife liked. We probably spent more wondering around Belize and Mexico looking then the lamps cost. Good luck, relax it will be fine.