The best tip i can give you is that expensive doesn't always look good. You can get cheaper clothes that look brilliant if you look on the internet.
www.asos.com and www.topman.com are two good sites that i use.
My style is i sometimes wear a fitting vest underneath a short sleeve shirt in summer, and when it's colder i wear long sleeved shirts underneath a v neck knit. Couple with dark wash straight leg jeans (or skinny jeans if you can pull it off), and some shoes/plimsolls to go with.
I mix and match, so i can look very smart, or very casual, or smart-casual, which is what you're after. If you only have black clothing inject some bright colours into your wardrobe, not neon bright colours, more pastel colours to start with. Make sure the items fit you, as i made the mistake of wearing clothes a size too big in my younger years, and consequently my clothes looked baggy on me, which doesn't suit anyone imo.
Keep things simple to start with, going overboard with trilbys and waistcoats peacock style might be too quick of a change. Build up your wardrobe so you can alternate items of clothing with each other, and not rely on one outfit that works together.
I don't profess to be a fashion guru, but i can spot things that will look good on me, and when i can't afford to get them i feel gutted.
