(Note the specifics given here apply to Band Reviews in Northern California. While much of this will apply to your area, be sure to always check the competition rules for exact information.)
The competition area for most band reviews is 450 feet long. The salute line is usually placed 250 feet from the step-off line (this is not always true. Many parades do not have full size competition areas. Check the rules for each parade or review to be certain).
Stop the first row of the band on the step-off line. You should stand about one half of the width of the band, in front of the band. When given the go ahead signal, start your step-off sequence.
While you may want to do some flashy twirls for your step-off, make sure you get the band moving quickly (Some reviews give a penalty if the band isn't marching 30 seconds after the go-ahead signal is given).
After the step-off you may want to do some twirling for the first phrases of the music. Then begin beating time. As you approach the salute area, begin your salute sequence. Salute the Reviewing Officer. After coming out of the salute, begin beating time again. Continue beating time until you are out of the competition area.
That's all there is to it.
Remember that at all times you want to look confident and display a great deal of poise. Look the part of a top level drum major.