Best done in the sunshine, with a stool to sit on

Lay the fleece out on your board, cut side up, after you've skirted it. Check for fibre strength by 'snapping' a small lock next to your ear - you're looking for a clear sound - if it's a soggy and dull sound then your fleece probably has a break in it and won't be judged. Check the fleece is nice and open with no matted bits. Check all over for double cuts and remove them, plus any veg matter you can see on that side.
Turn the fleece over, so it's now tips up

This is the bit you will be best to sit down for. Go over the whole fleece checking really carefully for all veg matter, especially around the neck. If it's not removable easily then use a different fleece to show, although you could pick out the ok bits to spin yourself. Checking for veg matter can take at least an hour unless you have a really clean fleece.
Before rolling, tear off enough britch wool to make the whole thing a bit more oblong - it's usually a bit wider at the bum end than at the shoulders. If you don't know which end is which, sniff it
Make sure the fleece is laid out with no gaps between staples because rolling emphasises this and opens up the roll so it looks really scruffy. Roll it by turning each long edge in so you have a three layer thick sandwich, then roll not too tightly from the britch end, but tightly enough to fit into the supplied bag. Before you roll, double check the show's requirements for rolling. They always want it with the butt ends visible, tips inside the roll, but some want it a la Wool Board with a twisted rope of neck wool wrapped around and tucked under itself to secure the parcel. Other shows want no neck rope, so just roll it to the end and it sticks to itself by magic. If the show bags (they should send them to you) is a plastic bin bag, then don't put the fleece in this until the day you take it to the showground, so it doesn't sweat.
Good luck