I would go with what you like and extend on that.
If you like jeans then get a really nice, stylish pair. Topshop are amazing for them.
Then some colourful basics. Basic vests, you can wear them under things and just on their own in summer. Still casual but a bit more colourful. Most shops (including supermarkets) all sell them.
Wrap tops are totally in at the moment so I would maybe try and get one in a neutralish colour (cream, black, brown...) they are very flattering for big boobs as well.
I would get a nice summery skirt. Gyspy skirts are in and most shops have them, Select had some nice cheap ones. I would get one in black just because it goes with everything.
Pointelle knits also rock my world, either as a shrug or a cardi, they look fab over coloured vests.
Ohh and combats. Next have some nice ones, as do River Island.
Turquoise, green, brown and white are all in this summer so if you get maybe one or two tops in those colours then you can pair them with your basics.
I would also get a denim mini because they are so fab. Casual with flip flops/boots and a tee or dressy with a nice top.
Peacocks is good for cheap up to the minute fashions. Basically I would look round the shops and see whats in and try a range of stuff on and then that kind of gives you an idea of what you want kwim? Sometimes I am surprised by what suits me and then from that I get ideas.