In our recent attempt at the Moraine for Life Adventure Relay, we encountered a lot of sand.
Some of these areas once formed shores of Lake Iroquois, so when I say it was like riding across a beach I mean it very literally - it was once a beach!
We had varying degrees of success getting through it, but in the process learned a fair bit.
I also found this article very useful.
Lesson #1 - Use wide knobby tires
We used two different bikes - a hybrid and a mountain bike. My hybrid had narrow cyclocross tires, the mountain bike had wide knobby tires.
Winner - mountain bike.
It might have been different if things were hard packed, but in sand you need a wide surface area to prevent the bike from sinking in. On the hybrid, I was left searching the edges of the trail for anything remotely solid to keep me near the surface, but often there was just nothing... it was awful!
Lesson #2 - Keep moving and pedal fast
Downshift, downshift, downshift... a quick cadence with even pressure helps keep on top of the sand. Sudden acceleration will dig deeper and kill your momentum.
Lesson #3 - Steer gently
There will be the odd jerk in fear to correct what look like an imminent fall... that's hard to avoid! But in general the key is not to move the wheel suddenly, or you dig up sand and sink.
Lesson #4 - Find the grip
Some trails I was on had deep sand in the middle, but the edges had vegetation holding things together. In other cases there were ruts where vehicles had passed that were a bit more packed and had better grip.
It takes a bit of trial and error to figure out where the traction is, but it's often worth a shot.
Ultimately, you can read tips on blogs and forums until your eyes turn red... but it's experience and practice that really give you the feel for what works and what doesn't. I'll be ready for next year!