Trying on a Jersey:
Do not wear a tee shirt underneath. The jersey should stretch a bit on your back and waist as you put it on. If you have trouble zipping all the way up or you can't raise your arms up, the jersey is probably too small. If you can pinch any material under the sleeves, on the chest or along the zipper too easily the jersey may be too big. When you bend over you should get very little drapery folding.
Modern high-end jerseys have short bodies and are designed to be worn with bib shorts. The jersey should come down to about 2 - 4 inches below the belly button. When you are in a cycling position, tucked over, the fit will change and will be lower than when you’re standing. The short-waisted jersey also helps prevents the dreaded "stomach wiener" effect that results from extra fabric draping outward in the riding position.
"Laser-cut" sleeves end in a smooth straight line with no sewn hem or cuff for a clean look and smooth finish. A properly fitting sleeve should be pretty tight, with some compression so it requires a little pull to get on, but not a big effort.
A laser-cut sleeve is quite long and should go almost to the elbow when the jersey is first put on. It will move up a bit as you ride. If any material hangs off the end of your elbow or if the end of the sleeve goes past the elbow, it's too big. If you can see wrinkles or creases around the shoulder and chest it's too big. If you have trouble getting it over your biceps or shoulder, the jersey is probably too small.