A few tape measure tips from a pro
Steel measures are much more common than cloth. Stiffness and convenient storage (and spring retraction) are steel's biggest advantages. Cloth tape measures are lighter, and better at measuring curved surfaces. and circumference. Which is why tailors prefer them. You also find cloth on very long tape measures, say 35 meters (or 100 feet) that are used for site work. This writeup will primarily concern itself with steel measures.
In purchasing a tape measure always purchase a measure with a blade one inch (25 mm) or wider. The reason for this is that you may wish to measure across open space. For example, if you are in your basement trying to run a gas to feed your new water heater you may wish to measure horizontally across the joist in order to find out how long of a pipe you need. The wider blades are less likely to droop. It helps to hold the blade with a slight pitch across its width, because that stiffens the blade, and allows you to extend it farther.
To measure from a floor, or upward, put the tab of the tape on the ground and stretch it upward with the tape body itself below the level of what you are measuring. Essentially, you use the tape that way so you have two tape widths supporting the tape's mass. Try to keep the blade level or plumb, as appropriate for what you're measuring. if you measure at an angle, your measurement may reflect the hypotnuse of an improptu right triangle, and thus prove inaccurate. The tab is loose, and will move the exact width of the tab, so you get the same measurement wether the tape is hooked on an object or butted up against it.
In the U.S. almost all tape measures have the inch number outlined in red every 16 inches. This is because in most construction studs are spaced sixteen inches apart, making stud-finding easy for the arithmatically challened. Every 18 3/8" there will be a black diamond for the same reason. So tape manufacturers do what they can to make your work easier.
Tape measures break. Their finite lifespan explains why only Sears guarantees their Craftsman brand tapes, at least in America. But there is one thing you can do, to slow your tape measure's inevitable death. Most tape measures have a return spring, which automatically rewinds them when released, unless the latch has been engaged. While it's fun to let a crisp tape snap back and closed, you should slow the tape so that when it finally closes it does so gently. That preserves both the spring, and the tab, which sometimes does break off at the tip. Spring and tab failures are the most common cause of premature death among tape measures. The blade may also tear, which will eventually prove fatal. However, gentility in rewinding and care in extending the tape will ensure a slow, lingering end. Which is exactly the kind you want when you've discovered a tear in your tape early in the workday.
For light or occasional use, a twenty foot (seven meter) or longer blade should be plenty. (I generally use a 25 footer) With proper care the measure may prove nearly immortal in light use. No toolbox should be without one.
Because of Sears's guarantee I buy my tapes there. If I'm exchanging them I try to return the favor by wearing something that indicates my status as a construction worker. Not all their tools are of professional quality, but enough are that I'm willing to give them the advertisement in return for a new tool.
Thanks to rootbeer277 for some excellent suggestions.