I've driven lots on sand - beach sand, sand dunes, hundreds and hundreds of dune crossings on the canning stock route. The key is air down, drop to at least 18psi to start with and then drop a couple of psi at a time from there as needed. Different tyres and vehicle weight etc will also affect what psi is good for a particular vehicle.
Get stuck and you air down some more, try to do that BEFORE spinning/digging down to the chassis. Take a full size shovel.
Not all sand is the same, place to place or day to day. Wide tyres are good, lots of power is good, keep momentum/speed as you hit a dune. Never try to turn around on a dune unless you REALLY know what you are doing - back down if you don't reach the top. ALWAYS slow down as you approach the top/crest unless you really know the other side isn't a windswept cliff. Sand flags are good.
Practice, practice and more practice is the key to learning to drive on sand and what works or doesn't. One good thing with driving on sand is that it is a lot more forgiving than driving on rocks - but you can still do serious damage if you forget to engage brain before gears...
Also, when turning on sand - turn before you need to turn - the vehicle will be directionally sluggish. If following in other wheel tracks the vehicle will want to stay in them - so plan accordingly.
Make sure you vehicle's cooling system is in top shape - slogging through sand works the engine. It also puts strain on the whole drive train so you'll find any weak points sooner than later
Like Cruiserdrew mentions above - even a 2wd can go surprisingly far with aired down tyres. Most VW beach buggies rely on skinny fronts (for better steering control), wide rears and good power to weight.
Don't be scared of sand - it can be heaps of fun to play on - isn't that one reason we drive 4wd's ?
cheers,
george.