Here are some tips that will hopefully keep you dry during a rainstorm:
1. Always check the weather forecast prior to leaving and once again when you get there. Understanding the type of rain to expect may even determine whether you go or not. If the forecast calls for severe thunderstorms with tornados or hail, you will probably plan differently than you might for scattered showers.
2. Buy the right tent. How can you find out? Read user reviews of the tent. Many unhappy tent buyers are happy to slam the tent in a product review if their tent leaked on them all night.
3. Once you buy the right tent, use a waterproof spray and make sure to seal the seams with seam sealer; even if the tent states it’s waterproofed and the seams are taped.
4. Never set up your tent in a low lying area. Look for a surface which will allow water to run off.
5. Use a tarp under your tent. You should do this regardless of the weather, but when it's raining it becomes important. The tarp should not be visible under the tent, fold under the sides of the groundsheet so water running down the tent will not catch on the groundsheet and be directed between the groundsheet and tent floor.
6. Make sure that your tent is properly staked out. It should be tight enough to bounce a quarter off of the fabric. If the fabric hangs, water will puddle on it and start to seep inside.
7. Do not touch the walls of your tent when it is raining and make sure that nothing is pushed up against the walls. This will adversely affect the water resistant capability of the tent.