The key to riding in sand is a combination of keeping the bike moving and low air pressure in your tyres. Momentum is very important, especially in very soft sand, and you should try to keep your speed up and the power on in these conditions. You will find that the rear of your bike will slither and slip around, but you will become used to this in time. Try not to fight it but rather stay relaxed and loose, and concentrate on keeping the front wheel heading straight ahead. Dropping the air out of your tyres is also important, as this widens and lengthens the tyre to ground contact area, which will dramatically improve your grip. Reduce air pressure enough to bring your bike under control, as little as 5psi if need. Be warned that in this under inflated state your tyres will get quite hot and be much more prone to punctures and creeping.  

If things start to get tricky or you are beginning to lose control stand up and blast the throttle a bit until you get back in control. Try not to attempt any sharp cornering when in soft sand but instead, if necessary, carry out long, shallow turns. Again in soft sand keep away from the brakes, particularly the front, if you need to come to a stop then slow down using your gears. If your bike starts slowing and the wheels start spinning, prepared to do anything to keep it moving, including paddling with your feet or even jumping off and running beside it until you get your momentum back. If you do become stuck in soft sand usually your wheels will sink down into it and start spinning as you grind to a halt. Turn the engine off and lay the bike down on its side. Fill in the holes and pick the bike up again. Start the engine and get the bike moving a bit before you jump on board. Try to keep the sand flat and level in front of your bike and if necessary turn you bike around to face down hill before moving off.