When in doubt, I advocate many folks to "grow up" their look. Wear button up shirts instead of T-shirts. Shed the flip flops in favor of a nice pair of wingtips. Put on a nice wristwatch. Now, some people are fortunate enough to be in situations where they simply do not need to wear these types of clothing. Be it people who are constantly active and on the run, or perhaps artistic types that are encouraged to dress a bit more eclectic than the average "well-dressed" guy.
To me, these types of occupations or lifestyles are no excuse not to wear clothing that looks good, feels good, and fits well. Just because you're not sporting a blazer and tie doesn't mean you can't look awesome. Let me try to show you some great looks even when you don't have just a normal office job.
1. The active, sports man
Zip up hoodie, dri-fit T-shirt, fitted track pants, Nike frees.
I think that activewear can look great these days. All the dry fit, compression based clothing helps keep clothing slim,
2. The eclectic type
Whatever clothing you want.
There are two people that I think dress well, albeit a bit more eclectic than I would prefer. Pharrell and Andre 3000. Take a page from their book if you're in the mood. Sometimes when you have a very confident sense of personal style, you can still look quite good in even the most ridiculous or outlandish clothing out there. Just make sure it fits well, and you wear the outfit with the utmost confidence.
3. The rugged outdoorsman
Barbour jacket, chunky wool sweater, denim or cords, rugged boots.
Just because you're out in the wilderness doesn't mean you can't look great. In fact, so much of menswear today is about sporting that rugged outdoorsman look, even if going just to the office.
4. The lazy at home type
T shirt, sweat pants, beanie, perhaps a hoodie or sweatshirt, New Balance.
I don't know if you've been following menswear magazines these days, but T-shirts, sweatpants and sweatshirts are more prevalent than I've ever seen. You know, back in the Mad Men era, when men wanted to just lounge around the house, they would dress down into a sport coat. Boy those days are gone. Instead, feel free to wear a nicely fitting sweatpant or sweatshirt to look good.
Whatever the look, there's a way to make it look good. You don't always have to be in a suit and tie, right?