Mixing different patterns can get you into a lot of trouble stylistically. Stick with one bold pattern and compliment it by wearing everything else as a solid.
Wearing shorts that are too wide or too long make your legs look scrawny. Even if you have muscular legs, wearing baggy shorts will make them appear skinnier than they actually are. Go with slim-fit shorts that fall above the knee.
If you’re going to wear a button down shirt un-tucked, make sure it’s a shirt that was meant to be worn that way. Typical dress shirts are way too long to be worn un-tucked and doing so makes it look like you’re wearing a short dress. I’m a big fan of the Untuckit brand because their shirts are cut shorter and look way better un-tucked. I have several shirts from them and they’re super easy to wash and wear.
Wearing flip-flops out as regular footwear is unfortunately something I see a lot. It’s too bad because there are so many other options that are just as easy and just as comfortable. Instead of going with flip-flops, try a nice casual pair of fashion sneakers.
The last style mistake has to do with socks. Not much will kill an otherwise great outfit faster than wearing ankle socks. Go to your local shoe store or department store and look for no-show socks. This style of sock is cut a lot lower so it’s not visible when you’re wearing a shoe. This looks a lot cleaner than wearing regular ankle or tube socks.