It usually depends on the race distance for me, and also how much I've been able to train, ie how fit I am
marathon...start off as easy as possible and build up the pace according to how I feel at certain points
Half marathon...start off at a good steady pace and pick it up towards the latter part of the race
10k...start off quite fast, build up the pace quickly and finish fairly fast
5k...run as fast as I can from the off and as hard and fast as I can til the finish.. that's why I don't particularly like 5k's, they hurt!