In most university cities it is perfectly possible to find decent accomadation in August. Where do you think students who get in via clearing/insurance and don't have a place in halls live?
In general, I think being willing to live more than a 10 minute walk from the university will give more choice and lower prices!
I also second the advice that it is best to discuss attitudes to certain things, e.g. heating, bills, mess, washing up, guests staying over, socialising, parties, smoking, pets etc before agreeing to live together! Anyone who has a really draconian view on any of these things is probably not the best person to live with! Living in shared accomadation will always take a bit of compromise, and anyone who is not willing to negotiate about one issue (unless for a good reason e.g. health reasons for needing the heating on) will probably not be into compromising on others.
Definately ask the current students what the landlord/letting agent have been like (if possible), and try to get recomendations from third years, with a bit more experience under their belt about where is nice to live/what letting agencies to avoid.
Second getting the contract checked by the SU if they can. When moving in, definately check the inventory etc. This is often a way that unscrupulous landlords try to screw students out of their deposit- saying things are totally fine when they aren't. They should check it, make any needed alterations and then hand it back.
Finally, try to avoid contracts which are "jointly and severably liable" if you can. These make everyone liable for all of the rent, so if others don't pay/drop out/leave the house, then anyone still living there can be chased for their remaining rent.
Room allocation should be done by picking the keys from a bowl at random.