Advice: European GP (Valencia) 22/6/12

[AMG01]

I am going on holiday the week this is on, just down the coast and am planning on heading up Friday 22nd June for practise. I want to buy tickets in advance before I go to avoid queues etc on the day. What websites should I be using and what ones should I avoid? Any other general tips from anyone that has been and any grandstands I should try and get tickets for.

Been to Valencia before so no what the City is like.