Always look your best! Shined shoes (and appropriate shoes!), clean shirt, ironed pants that are for umpires (no, Dockers are NOT made for baseball umpires!!!
), clean ball bag, right colored T-shirt, CLEAN HAT! Wear the UNIFORM properly. Keep your shirt tucked in. Make your hat look smart on you, not like Gomer Pile! Make sure the pants are hemmed properly (1" break...this is why combo pants are a HORRIBLE idea! Your plate shoes will cause your pants to break higher than base shoes will, thus, you need to have them tailored differently).
Don't stand around looking like a underwear model. You know, that lazy stance where you have your hip cocked out to the side, and you look like you are "chillin'". This is a HORRIBLE look!!! Keep your big fat noggin' squarly between your shoulders at all time, and keep your weight balanced. It makes you appear to be ready and alert at all times (as you should be). Don't slouch. Hustle to every position, including when you go to brush off the plate after a pitchers warmup. A few "trots" to the plate looks like you are hustling, and really does help keep your head in the game.
YOU WILL BE JUDGED MORE BASED UPON YOUR APPEARANCE THAN ANYTHING ELSE!