IIWY, I'd try and work out my style first.
Then, do you want cheap and cheerful (Primark etc great for updating as are New Look) or do you want more middle or even high end?
Whistles are great for on-trend but expensive pieces which tend to last longer. Cos are lovely if you're taller and slim as are &Other Stories (seems to be younger and trendier than Cos).
I'd go into Oasis, Top Shop, Joules etc and just try on. Maybe go with a friend.
Create a look-book of stuff you like then either Pinterest it or post links to stuff you want to buy here. Skinny jeans, Ash Boots etc are popular here but they may not suit you and do you want to look like a lot of other people (not dissing people like that, I wear same!) or are you more Rock Chick/Emo/Sporty etc. Some women I know look fab in sports gear I don't, not much.
If it's basics for everyday and you want kid friendly stuff Hennes and Divided (their younger range) has great basics and fashion bits. Uniqlo good for basics too but I find them a bit boring. Sometimes TK Maxx turns up bargains. And places like Sainsburys, some great basics etc.
Then we have evening wear - again, do you go out with partner/girlfriends etc? Have a look and see what suits you. Do you like sequins, peplum tops etc?
Good luck. 