I've got a friend who always look very groomed and together, she always looks really great, and I'm very jealous! She hasn't got a lot of money but seems to wear classic clothes really well, just things like well-fitting skinny jeans with a coloured vest top, then a nice necklace or scarf (which she says are always from Primark). She also has really naturally good skin, which means she doesn't need to wear much, if any make up, and she's good at doing her hair in elaborate up-do's.
I'm thinking it's probably good quality classics plus the use of accessories that make a difference.