Working with flat tires is easier if you know these things:
1. First, make sure the problem is not just a loose or damaged valve stem. Put a bit of water or spit on a fingertip, and press very lightly against the top of the valve. If you see bubbles, you may need only to tighten or replace the valve core.
2. Use blunt objects to remove the tire, or you may end up with additional holes in the inner tube.
3. Feel carefully around the inside of the tire while looking at the outside. Whatever created the hole in the inner tube may still be sticking through the tire.
4. To be nice to the environment, try to patch the inner tube instead of replacing it. If you use a conventional patch kit with liquid glue, let the glue dry fully before applying the patch. This point is so unbelievable to many people who have not worked with contact cement that I will repeat it: Let the glue dry fully before applying the patch.
5. It is possible to replace most tires without using tools. Put just enough air in the inner tube for it to hold its donut-like shape. Set the tube in the tire. Check that the rim strip properly covers the spoke nipples all around the wheel. Push the valve half-way into the valve hole on the rim. Starting at the valve, and working around both sides of the wheel, finally meeting at the side of the wheel opposite the valve, press the tire over the rim. Once one side of the tire is on the rim, push the other side over the edge of the rim in the same way.
6. Push the valve toward the tire to make sure the inner tube is not pinched under the edges of the tire, then pull the valve stem out of the hole to its normal position.
7. Inflate the tire to just a few pounds per square inch (PSI). Inspect the tire all the way around both sides of the wheel to be sure it is seated properly. Then inflate the tire to its full rated pressure for street riding, and to a pressure of at least 30 PSI for off-road use.
8. Keeping tires inflated properly is important for the long life of your wheels. When you hit the edge of a pothole or a tree root with underinflated tires, the rims can become kinked.