How do to look good in a school uniform?

I have to wear a white polo shirt, a burgundy jumper, black shoes and either black trousers or a black skirt, and I want to try and look better in it. I'm a little bit fat, but not huge, so if you have any ideas on how to look thinner, that would be great too. I can't dye my hair, but I can wear some make-up and jewellery. Please help. :)