Oh Boy, Sian, do you speak the truth!Assuming that you're not so desperate for company that you'll put up with anything on two legs, these things should be paramount:
Forget having tons of similar interests....If he/she thinks that Bill Cosby talking to cute kids is funny, and you think it's nauseating.....the relationship will NOT work!
Find out what he/she laughs at.....listen closely to the answers....it's crucial.
Restaurants..another dead giveaway. If he/she treats waiters and waitresses with disdain.....you're next!
and my personal favourite: If someone has a penchant for treating "selected" people badly....it may take a while, but eventually you'll be one of the 'selected'.
Rick