I went around a bit recently, and the following is a few of the things I picked up:

Tear the cover off of your guidebook, photocopy the pages you need, or somehow otherwise hide the cover. I have no idea why the travel book publishers release books that have loud, fancy, obnoxious covers in which some variation of the words "Travel Book" feature prominently. Walking around with a travel book is bound to get you into trouble should you go anywhere other than the most frequented tourist trap, but especially so if you're going to use public transportation (and especially especially so if you're going to use the subway).

If you need to gaze at a map for long periods of time, it's probably a good idea to do it someplace private, or at least in an inconspicuous manner. Looking blatantly at a map for a long time in a public place is a sure way to become a mark.

Make at least a half-hearted attempt to learn about the currency. You should, of course, know the conversion rate to your local currency by heart, however, in addition, you should learn the general shape or color of the larger coins and bills. Bills are generally pretty easy because they have their amount displayed on them so prominently. Coins are harder to deal with, so you should get a rough idea as to what the larger coin denominations look and feel like. Unlike America, there coins that are worth in the vicinity five dollars in the local currency are in circulation, at least in Europe. When you come across a mendicant (as you surely will) and need to throw some money at him to get him to go away, need to quickly tip a waitress, or need to use the machine that dispenses tickets when there are a million angry people behind you, you need to be able to recognize your coins fast.

More about travel books: Don't trust them. I'm serious. I went around with two guidebooks (both of which were published within two years from then), and between the two of them, they were wrong five or six times. That doesn't sound like much, but when you have a few days in a city, wasting a few hours trying to figure out where the hell the shop you really wanted to go to is, why the museum isn't open, or why the tram isn't stopping where it's supposed to is a big waste of time. I don't really have a good solution to this. Calling ahead in the case of museums to find out their closing time is, of course, a good idea, but it is rarely feasible. Looking in the phone book would be nice to confirm the shop's address would be good, but, of course, you are almost never going to have that luxury.

Don't be rude. I'm deathly serious. This is very important, especially if you're American. Americans already have a bad reputation the world over for being loud, obnoxious jerks. From the other Americans I've seen on the road, this reputation often holds true. They bellow loudly. They cut in lines. They are generally nasty or clueless. Please, make at least a cursory effort to be nice and disrupt the locals' lives as little as possible, or, in the case of people whose job it is to deal with tourists, a little bit less of a hell. They will love you for it. They will smother you in kisses.

Ah, well. That's all for now.