I think I used to be pretty darn polished but, if truth be told, looking like that is time-consuming and requires quite a lot of effort in terms of well cut clothes, good shoes, decent haircuts, learning how to apply make up properly and so on. I haven't got the will, (or the body), anymore to be quite that soignée.
But there are some things that are useful.
A free makeover from your nearest Mac counter or similar, can be good - you'll have to buy one item but it's worth it to see the difference that well applied make up will have.
(If you're in or nr London) a friend of mine - who is the most well groomed person I know - gets her hair cut (and coloured) at Windle & Moodie, a renowned and chic hair salon for around £30 on model nights. Normal prices can run into over £300 for a cut and colour by a senior stylist ...)
A good local tailor/seamstress - getting your clothes altered to fit you once they have been bought is invaluable.
A few well cut pieces (your basic capsule wardrobe) that you can mix and match in colours that suit you.
An expensive coat in a classic colour (sales can be amazing and it should last for a few years, at least)
Shoes/boots polished and repaired as soon as they need it (no worn down heel tips or the like).
Clean, manicured hands, with a light polish.
Teeth (!) regular scale and polishes.
A good handbag.
See? Easy peasy :)