Servers should come to church dressed smartly and attired so as to complement the cassock and surplice that will be worn for the liturgy. This includes:
Black pants - so as to be indistinguishable from the black cassock
Black socks
Black dress shoes (or boots) - Sneakers, brown shoes, sandals, and anything other than black dress shoes are a distraction and draw attention to themselves.
White shirt or t-shirt - The shirt should be covered by the cassock and surplice, and should be white in case the edge of it does show. High shirt collars should be rolled down so they are hidden by the cassock. Many servers prefer to remove their outer shirt and just where a white undershirt under the cassock, especially in the warmer months, which is fine.
The ordinary vesture for servers is the cassock worn with a surplice.
Servers should arrive at least twenty minutes before mass starts. Once in the vestry they should immediately change into cassock, and any functions before the start of mass in the sanctuary or chancel should be done by a server wearing a cassock. It is amazing how the cassock immediately changes one's body language and carriage for the better, preparing the server to perform the dignity of his office.
The vestments that you wear, the cassock and the surplice, are actually clerical vestments now permitted to be worn by those specially-selected laymen assisting at the altar. You should always put them on prayerfully, with your attention on the sacred duties that you are about to enter upon.
Your cassock should hang a few inches from the floor, just touching the top of your shoe. If it is necessary to make a choice, it is better for your cassock to be somewhat too short than too long, because of the danger of tripping. When you genuflect in your cassock, it is best to move the left foot forward and keep the right foot stationary as you kneel. Always genuflect on the right knee. When you rise, keep the right foot stationary and draw back the left foot. In this way you are very unlikely to trip on your cassock by getting it under the foot on which you put your weight. If yo do not have room to move your left foot forward, then of course you must move your right back, but then you must be careful in getting up to keep your cassock out of the way of that right foot. This may require you to pull the cassock forward with your hand as you kneel and as you raise your knee.
In kneeling, the only sensible way to keep the cassock from tripping you when you rise is to grab hold of it and pull it forward away from you as you kneel. You must aim at kneeling down with the entire bottom hem of the cassock several inches in front of both feet. When you stand, pull the cassock out again, if necessary, to prevent putting either foot on it. A little practice is all that is needed to learn all this and for it to become automatic.
The surplice is worn outside the vestry when performing a liturgical function in the chancel or sanctuary or when the liturgy is actually in progress. The surplice should hang somewhat below the waist. Whereas a cassock should, if necessary, be too short rather than too long, the surplice, for appearance's sake, should, if necessary, be long rather than too short.
You are responsible for hanging your cassock and surplice neatly in the vestry closets. Cassocks and surplices should be hung according to size with smaller sizes ranked to the left and larger sizes arrayed to the right.
If a surplice or cassock needs immediate cleaning (for example if it is splashed with wax), you may put it in the laundry basket in the bottom of the surplice closet. The altar guild examines the vestments every week after mass and washes them regularly, so only put things in the basket if you feel they are in immediate need of cleaning. If a surplice or cassock needs mending, leave it neatly folded on the counter with a note.