Denim is usually sold using regular or tall sizing. The key measurements used is the waist measurement and your inseam measurement, which is the length from the crotch to the bottom of the inside of your pant leg.
While shopping for a new pair of denim, try on jeans that match your measurements, and look at yourself in the mirror from several different angles. Also, try tucking your shirt in and see also see how it looks untucked. Ensure that the fit is comfortable and that you are able to move around in them without feeling uncomfortable. You want to make sure they feel good on you. It is also a good idea to make sure you can fit your thumb in the waistline, to ensure you don't feel discomfort sitting down or after a big meal.
The cuff of the pants should not touch the floor. In the case that it does, by simply taking them to a tailor, they can be shortened to a length that not only looks great but doesn't wear out the bottoms. On the other side, you do not want pants that are too short either. If the cuffs are touching the back of the shoe then you have found the perfect length for yourself.
It is important to try on all jeans before you purchase them. Even if you buy the same brand, it is common that different styles, even by the same brand, can fit differently and may fit your body differently.