the contract usually covers the major issues such as bill payment, PUB arrangement, whether cooking is allowed, whether friends are allowed to stay over etc. which is pretty straightforward - sign it only if you like it.
most inconveniences though, usually arise from day-to-day activities by inconsiderate flatmate(s). having a person-in-charge in the house is better, as opposed having person-in-charge who is only coming over now and then. flatmates whom you think you can communicate with (similar age group, similar situation etc.) are usually easier to deal with than ones not. the more detailed 'rules & regulations in the house' mentioned usually indicates better household. of course, none of them guarantees a happy ending.
the golden rules: no more than 3 persons including yourself (you may want to allow weekenders
but only 3 of the permanent residents) and ALWAYS include the early termination process in the contract - insist to add one if there is none.