Done a few of these in the past - they are great fun.
However I am giving it a miss this year. £30 is too expensive for me.
The main tip I offer is look where the people in front of you are running - let them find where the deep water is. Also the puddles - the middle can often be shallower than the edges as that is where the tank tracks/vehicle wheels go. And if you want any sort of decent time, then get close to the front for the start - the first couple of km are quite narrow and too many people near the front walk - often 2/3 abreast. Fancy dress always goes down well with the spectators but do make sure its something that can get thrown in the bin afterwards as it will get trashed.