Traction is always important. My dear old dad always used to tell us that "the only horsepower that matters is the horsepower you can put into the ground," and nowhere is that folksy motor-head wisdom more relevant than in the sand.
If you've had your quad in storage waiting for desert season it's a safe bet that after months of sitting idle while subject to varying temperatures and atmospheric pressures will cause even new tires to leak a bit. Check to ensure they're all still holding air, and fill them up (or bring them down) as needed.
Tire pressure should be adjusted to match the conditions you will be riding in. If you're riding in sand you need to know that the drier the sand, the lower you will want to set your tire pressure. Anyone who's spent any significant amount of time in the dunes will tell you that sand conditions shift like the sun and stars.
What may have been the right pressure settings for your tires in March may not be right after a long dry summer in October. Best to check the weather forecast (and maybe how much rain the area you will be riding in received over the summer) and make your determinations accordingly.
In addition to the terrain features and riding conditions, specific PSI (pounds per square inch) settings will obviously vary based on the type of bike, paddle tire or knobby tire, tread life, tire size, individual preferences, etc.
Generally speaking you will want to run knobby tires at a lower tire pressure than paddles, especially in very dry conditions. Do keep in mind that ATV tires are tubeless, so you don't want to run them down too low, as it's possible to run a flat off the rim completely.
For knobby tires it's a good idea to keep the pressure at a minimum of 2 PSI, for paddles the number should be closer to 3 PSI or higher, but again, how low you need to go depends mainly on riding conditions (these pressure recommendations are for dunes, soft powder sand, and mud where firm traction becomes a paramount issue.
For hard pack/track conditions where flotation and traction are more assured, the PSI setting should be higher). Remember the general rule of traction for off-road tires: Higher PSI allows for less resistance against the motor as it spins the tire, but lowers the level of flotation/traction. Lower PSI will create greater traction and flotation, but also greater rotation friction at speed. Balancing these competing forces based on your ride, riding style, and terrain conditions is the key to traction success.
It's also always a good idea to have some sort of pressurized air source to take with you. Portable air tanks are fairly common and relatively inexpensive. If you don't have or can't find an air tank, go to any auto parts store and purchase a can or two of fix-a-flat. It's a pressurized can of puncture sealant designed for street tires, but it works great for filling up low pressure ATV tires. This is especially important if you will be riding at an elevation that significantly differs from home.
The amount of air pressure in your tire will vary based on your relative distance above sea level, so while you might have the PSI reading you like in your garage, it's a good idea to re-check and adjust accordingly once you've arrived at your riding destination.
This is a simple yet often overlooked step that will keep you floating on top of the sand rather than sinking into it. Make sure that whatever PSI level you choose for your tires, that it closely matches the other tire. Uneven tire pressure will make your ATV drift when in motion and can increase the likelihood of a rollover or wreck, especially when riding over uneven terrain.
Tires that are properly maintained, adequately and evenly pressurized, will increase your bike's performance while promoting safety and maneuverability at the same time. While this is quite possibly the quickest and easiest pre-ride maintenance task, it is also one of the most vitally important, so riders would be wise not to overlook it.