If you want this look, inspect your clothes, coats, handbags etc and don't wear any that are starting to look shabby or tatty round the edges.
If you get good quality leather handbag, shoes etc, even if they're not "designer" they'll last longer before looking scruffy.
My cheap, non-leather handbags often start looking tatty round the edges, piping peeling away slightly, parts of the fabric wearing off etc, whereas the real leather ones continue looking good.
You don't notice these things at a glance but overall it gives you a less polished look if you don't pay attention to these things.
Research high street clothes that "expensive" people wear e.g. Kate Middleton (they dont wear designer all the time!) and buy clothes from those stores heavily reduced when the sale is on.
I am not normally this superficial but I have had to think about this a lot due to visiting in laws who run a luxury hotel. I can't go there in clothes that scream Primark and charity shops!
50% of my clothes are from Primark, cheap shops, and charity shops, 25% from middle range high street stores like Topshop and Dorothy Perkins, and the remaining 25% from 'expensive' high street shops like Hobbes, but I get those in the sale. Its the way you put it all together!
Another easy option is to wear all black and accessorise with your best jewelry.