Since the average business traveler may not be familiar with the folkways of the kinds of establishments we discussed above, here are some hints on how to act, how to dress and how not to give yourself away:

Don't phone for reservations. No one likes a wise guy.

* Don't expect valet parking. You wouldn't at Burger King, would you?

* Don't overdress. Jeans are okay everywhere. Jackets and ties are a bit odd at the Trio and practically invite confrontation at Millie and Al's.

* Don't assume you'll be shown a seat. You may be, or you may not. Be cool, and watch the regulars. Even at as a funky a place as Food for Thought there's often someone to seat you. But at least they have a sign to warn you.

* Don't expect a hat check girl. This isn't Fred Astaire, 1935.

* Don't bother looking for the sommelier.

* Finally, amidst all the don'ts, a do. Do tip at least as generously as you would anywhere else. If Pierre's is worth 20 percent, then so is Jose's. no-smoking section, wonderful salads -- like the comprehensive veggie chef salad ($3.50) -- and an entertaining community bulletin board. Hot specials daily; check the chalkboard as you come in, or as the menu says, ask your waitperson. Music nightly runs the gamut; they pass the hat between sets. Gordon is the city's tallest waiter.

Just down from FFT is a restaurant with an unlikely name: Cold Duck (1732 Connecticut Ave.). Regular American food here, with Cincinnati chili ($1.85) and pan-fried chicken ($4.25 for a half chicken) co-starring with the ribs ($4.95 when available). The sign on the door says this is "VFW 9619 Annex."

Your waitress at the Trio (17th and Q Streets) is likely to call you "hon" and will serve you a multicourse dinner like Mom used to make, right down to the Jell-O. The menu changes daily and you can expect change back from a five.

Washington restaurants don't come much smaller than Tien Yuen (1612 16th St.), but they don't come much friendlier, either. It's an unassuming, one-woman operation, with nice touches such as linen tablecloths and napkins. I like the spicy Mongolian beef ($5.25) and the chicken with peanuts ($4.80), both prepared as hot as you like.

Kramer's (1517 Connecticut Ave.) is wonderful for after dinner. Browse in the bookstore section for a while and then head back to the cafe for drinks or dessert -- strawberries and rum with whipped cream ($2.50).

Beer drinkers might want to end their evening at the Brickskeller (1523 22nd St.), a basement saloon which boasts hundreds of different kinds of beer. Not a real classy establishment, but the only place hereabouts where you can answer the time-honored question, What does beer brewed in New Jersey really taste like?