Finding drinkable water is probably the biggest challenge to surviving a desert environment, but you'll first want to look for plants and animals, including leafy trees (not cacti), insects and birds. These all require water to survive, and they might point to a nearby water source. Getting to higher ground in order to get a view of the landscape may also be helpful for locating water sources in deserts.
Topographical maps and compasses can help to find water sources in north-facing canyons and depressions, which are protected from the sun and do not experience as much evaporation as other parts of the desert. The prickly fruit from cactus plants may provide some hydration, but drinking liquid from the cactus leaves themselves can be more harmful than helpful.
Ultimately, though, the best strategy is to enter the desert with more than enough water to ensure no emergency situations occur. Those who find themselves stranded with no water may want to avoid physically strenuous activity in order to find water; sweating can make dehydration worse, which shortens the amount of time a person can survive in the desert.