Do not be influenced by flashy uniforms. Be suspicious of dojangs that use uniforms that are too different from the norm.
Appearance of Instructor
A skilled Taekwondo fighter will probably be in excellent physical condition. A skilled Taekwondo instructor may be a physical wreck. When you are in need of medical attention, you do not care whether the doctor helping you is fat or not, you only care whether he or she can help you. Similar to good coaches in other sports, good Taekwondo instructors come in all sizes, shapes, and levels of fitness.
Trophies are nice for the people who earn them, but do not be too impressed by a large collection of trophies in a dojang. Anyone who goes to a lot of tournaments will have a trophy, sometimes you may be the only person there in a belt/weight/age class so you get the first place trophy. If you are interested in the trophy collection, read what is on each trophy to see is it is an important one. Also, consider the ratio of trophies for sparring and patterns. This will give you some indication of which the school gives the most emphasis, sparring or patterns.