Decent 'sweat wicking' material would be my advice and colours that match - or one colour overal (my Asics gear is black with red trim)l.
And don't forget to get the right type of running shoes: have a gait test at a specialist running shop if you haven't already done so. Your legs will thank you for it.
Avoid the very top makes like Adidas and Nike, because they'll rip you off. I got my running stuff from Sports Direct (Asics) - and I recommend you do the same; there are always wonderful bargains there. 
For when it gets very cold, a full length pair of running tights - I wear shorts over mine, otherwise it feels a little bit like going out in underwear.
I'd advise against tracksuit bottoms - they just get horribly sweaty.
Edited: 03/12/2012 at 13:40