Some really great advice all around in this thread! You'll do fine. As for a loupe, I carry one to shows that has a built in bright LED. It helps a lot. The pinpoint light tends to make the coin look worse than it really is, so if it still looks good to me I know I'm going to be happy with it when I get it home. For negotiating, the most important part is to know how much what you're selling or buying is worth. Do your research before going to the show. Look at eBay/Heritage auctions to get a feel for the market rate. Also pick up a greysheet (I usually buy one issue back because it's a lot cheaper, within a few days of going to a show). That way you have a good idea of the wholesale values as well. If you know a coin has been in a dealer's inventory for a long time, the dealer is likely to negotiate more. Likewise if it's the end of a show and it's been slow, they might be more acceptable to offers. I've bought a few coins at nice prices where I've not been interested at what they were initially asking, but when I came back at the end of the show they were more willing to deal. Sometimes a coin is so overpriced though that it's best to just say thank you and walk away without making an offer. If it's the right coin but the wrong price, don't be afraid to walk away. With the exception of extremely rare material, you're likely to see one again, especially with internet sales.
Remember, most dealers are friendly...they should be if they want to get your money, and they are interested in coins or they wouldn't be in the business. Make sure to check out those junk boxes and half-priced bins, sometimes treasures are there.
Being polite and friendly never hurts. Remember the Golden Rule, "Treat others like you want to be treated." Always seems to work for me.
Re: Loupes. I'm not that interested in RPMs or errors, so I only take a 4x loupe with me to shows. And, really, it's not all that useful for grading except to confirm the presence of hairlines in an area I've already spotted by rotating the coin under light.
Well you've had lots of suggestions but I'd add to think about doing a trade on that indian ad you might make out better.
Consideration. If a dealer gives you the courtesy of taking out a piece for your examination and time to look at it, don't be upset if his attention turns to another customer; appreciate the fact he didn't hover over your shoulder. In addition, when done examining said piece, get his attention to give it back. Don't just set it down and wander off to the next table because if it disappears you are the last person he saw with it. Courtesy goes a long way.
Dealers don't have a lot of room to display stuff so they keep some under the counter. Some dealers will ask what you are looking for so they can pull it out for you. Nothing wrong with asking if they have anymore of something tucked away.
I've got too disagree with the phone part. For the most part most dealers don't care if you are looking at a phone or laptop as long as your not doing so while having a conversation. My friend took his laptop to the show we went to last and there were no problems. Oh and if there are boxes of coins and books or albums laying around on the tables don't be afraid to look. That is why they put them there.