OP, if you currently wear jeans and baggy tops, and don't think that skirts/dresses suit your lifestyle, here's what I'd do:
Get a couple of pairs of really good jeans. This takes quite a lot of work(!) but once you've found some that fit you well, get more than one pair! Personally, I like straight or even bootcut, but you might prefer slim or skinny. Experiment! Try on a ton of pairs. Also, wear good knickers with them.
Invest in some fitted tops. These don't have to be tight, but try some that actually fit closer to your body. Show off a cleavage if you like. Work out what colours suit you. Don't think they have to be long enough to cover hips/bum/whatever - people can still see what size you are, whatever you're wearing. If you're tall, longer length tops can be good, if you're shorter, I'd avoid them. But again, try on lots of things and see what works for you. Aim to get a mix of casual and smarter things. If you try something on and it makes you smile, buy it.
And then, get great accessories. Shoes, bags, jewellery, whatever - you can buy these anywhere! I love going into skinny girl shops and ignoring all the rude stares to get a good bag or scarf or something.
Have fun!