Shirts
Unbutton shirts when you wear them, and put a white or black tee underneath. Solid tones are ideal choices. Better go without cartoons on the tee. Logo tees are acceptable, and can be considered an occasional highlight.
As to patterns, you can choose solid colors which make people look neat and clean, as well as polka-dots and stripes.
If you insist on checkered shirts, smaller checks can give you a slimmer look. Remember the best checkered patterns are those that will not remind people of an old bed sheet or tablecloth.
