Look around online or flip through some magazines to get a since of what you want and then set up appointments to go shopping. Most bridal stores ask that you make appointments when wedding gown shopping. Call ahead to your local stores to make sure they will let you look or try on gowns. Look at different shapes; A-Line, ball gown, fit with flare, etc. Necklines; strapless, straight or sweetheart, halter, small straps, V-neck, etc. Think about colors; sash and corset back are easy ways to add a little or a lot of color to your gown.
Same goes for caterers, bakers, event spaces, florists, musicians, etc. Also, ask for references or samples of the work. Make sure you get along with everyone that will be spending your special day with you.