Gentlemen, a few things to keep in mind about your dress shirts

We've seen some bad dress shirts. Don't pretend you haven't as well.

You've seen the guy at the office with the untucked billowy shirt.

You have the friend who still thinks it's okay to wear a dated black, striped dress shirt out to the bar. He is unaware that he looks like a member of Smash Mouth.

Most bad dress shirts fall under the categories of, too big; too wrinkled; wrong color; wrong fit. A bad dress shirt can make you look sloppier, fatter and cheesier than you ever want to look.

So we at Business Insider asked our friend Jessica Cadmus, stylist and founder of site The Wardrobe Whisperer, for her thoughts on dress shirts. 

Surprise, surprise, there are some simple rules - a few things to keep in mind as you're shopping or dressing - that will make picking something out a lot easier and make you look a lot better.

Understand when it's time to (un)tuck

"As a general rule, if the shirt is long enough to cover your bottom, it is meant to be tucked in," Cadmus told us. "Having said that, many shirts are cut shorter these days in order to avoid excess bulk when tucked - these are the shirts that cause confusion. In these instances it's important to listen to the subtle language of the shirt itself... For instance, if the shirt bottom has notches on either side, these indicate its ability to remain untucked (this is a "finishing" detail). "

"Similarly, if the shirt bottom is cut straight across in the front and back, the intention is for the shirt to be left untucked.  If the back is sloped, likely it was meant to be tucked.  If you are unsure, tuck it in.  Better to look overly polished than dumpy."

Do not buy a pattern everyone else is wearing, for the love of God

Remember this?

There's a way to mix patterns without looking crazy

Here are the rules for that:

1 - Mix a large scale pattern with a small scale pattern

2 - Make sure the patterns are in the same or complementary color families

"So, for instance," said Cadmus, "a functional mix would be a navy suit with white window pane pattern (large scale), a solid light pink dress shirt, and a navy tie with small scale white polka dots."

Get the fit correct 

This is for you, billowy shirt in the office guy. Your shirt is too big, bro.

"Dress shirts stand at the core of a man's wardrobe considering, on average, he wears them 5 days per week.  Therefore it's essential to nail the fit. Take the time to have yourself measured by a professional," said Cadmus.

A few pointers she left us with:

• When the neck fits properly, you should be able to get no more than one finger between cloth and neck.
• The shoulder seams should line up with the end of your shoulders. 
• The cuffs, when undone, should land approximately halfway down your hand. 
• And the body should not have excess volume in the chest/torso area, nor excess length. Many shirts now have a small amount of stretch in them which assists with a closer fit.

Do yourself a favor - make sure your shirt's fabric is not sheer

If you don't have time to try a shirt on, test it against your hand, Cadmus suggested.

And yes you must wear an undershirt. She recommends Tommy John "because of the form hugging fit which does not contribute to bulk under a shirt. Incidentally wearing an undershirt also extends the life of your dress shirts because they wick moisture and will take on any stains prior to the fabric of your shirt discoloring. I'd rather replace a t shirt than an actual shirt any day."

Do not wear yellow

Oh yes, please don't.

"Unless your skin is a rich and luxurious color like that of, say, Idris Elba, please do not attempt to wear a yellow shirt," Cadmus said. "Pale skin and a yellow button down screams one thing: I AM AN INTERN WHO ONLY RECENTLY STARTED WEARING GROWN UP CLOTHES."

There's also a debate raging at BI over whether or not dark colors are acceptable. There's an argument to be made for the fact that you are not Johnny Cash or a cast member on Jersey Shore. Use your mother's judgment on that one.