At work do not wear oversized shirts, it looks sloppy, find out which cuts is fitting to your body.
If you are not wearing a tie or a bow-tie with your shirt, leave the top 2- 3 buttons up, it will give you a nicer neckline. Another idea is to wear a scarf.
Large collars shorten necks.
Button down shirt collars look better without ties.
A must in your wardrobe is classic white shirt, it works with everything, it`s a multitasker and will always look sharp.
If your face feature is long, wear shirts with a spread collar, button-down collar or a tab collar, it will fit you best.
If your face feature is square, shirts with a button-down collar or a rounded-point collar will fit you best.
If your face feature is oval , choose, avoid shirts with round collar.
The sleeve of your shirt should be a bit longer than your jacket,
If you have a long neck, wear shirt with high collar fit.
Have the top 2-3 buttoms up if you have a short neck as long as the purpose to wear a shirt allows it.
Remember to choose colored shirts according to the colour of your skin, eyes and hair.
Get inspired, look at the different collar`s shapes
Photos source: menswearmensrealstyle
Photo source: Terrence Sambowrites