Are you wanting to buy now or in the sales?
General tips, hmm. Well, first and foremost - avoid matching shoes and bag, is dated and frumptastic.
I'd say it's well worth taking the extra time to hunt out for something with sleeves, it saves you from the near impossible task of finding a cover up that works, is warm and isn't too bulky. More importantly though, it usually looks more stylish and less cluttered. Definitely avoid things with matching wee jackets will age you horribly.
Fascinatiors are the work of the devil, almost without exception. Wee hats OTOH are grand (big hats too for that matter). But, there's usually no need for headgear unless you fancy it.
Good underwear is 8/10ths of the battle.
erm, dunno, loads of stuff.
Will have a rummage for ideas, what sort of budget are you on?