Most Helpful Girl
No need to improve your fashion sense.
Just define your style. [:
Your style should be able to say something about you. Whether you're a chill-type of guy, business-y type, etc..
I do have to ask you for an example of the type of Hawaiian shirts you were, are they like Tommy Bahamas? link
And bowling shirts?
I think olylowlife has a great idea too. Don't need to go Downtown, however. You could just stroll through a mall.
Perhaps scroll through Lookbook and determine what you like. link
Since you say you're not in the best shape, I think you should invest into a good pair of DARK jeans. Probably bootcut or straight leg. They don't need to be expensive $100 jeans. Just something that's made well, doesn't look cheap.
Please no baggy jeans. They never look good. Just don't go there, okay? Hah. :]
I place I personally love is Gilt and Hautelook.. Great designer products that are up to 80% off. Only downfall is if you'll not into buying online. They both have excellent return policies however. [: And sizing charts for all of the products sold. link link
All in all, I think the best thing you can wear is a smile and confidence, and this is coming from a fashion major. [:
Best of luck with your style choices.<3
Hope I helped in some way. :]