So, what is the right length? Probably we'll just put on our shirt and walk. This little detail will determine how good looking are you otherwise it will definitely destroy your look even if you put on an expensive and branded shirt.
A tips on how I determine the shirt's length for me. I would use the level of belt to judge what is the right length, somewhere above or below that will look perfect for me. If the shirt is too long for you, your body will look small and short.
On the other hand, if you want to go slightly formal or gentlemen, you can always tuck in your shirt and match it with a nice looking belt.
Pick the right belt if you want to go either tuck-in or un-tuck, it will definitely give you some extra score on your outfit.