The correct way to use a tape measure is to read from large to small. Most measurements are whole-inch, half-inch or quarter-inch marks. These three marks take care of most measurements.
The longest and only numerically-indicated mark on the tape is the whole inch. It's the easiest mark to see and use. The second-longest is the half-inch mark. This mark falls into the "no numeral" zone, but it divides the inch into only two parts and using it is a simple calculation. Next comes the quarter-inch mark, the third longest mark that divides the inch into four sections.
Next smaller is the eighth-inch mark, which divides the inch into eight sections. Measurements this fine should be written down, as they are difficult to memorize. The smallest mark on the tape measure is the sixteenth-inch mark, which is so small that it's probably best to measure to the closest eighth-inch mark. For example, when measuring 6 7/16 inches, first measure to 6 1/2 inches, then measure down slightly to the nearest eighth-inch.
As a rule, measure twice and cut once. For even greater accuracy, measure thrice and cut once. Another way to ensure accuracy is to make sure the tape is firmly hooked or butted.