We don't get too much sand/gravel here in Edmonton, so I turn to friends on 
the mtb mailing list for help:

Peter Greaves [greaves@ccmail.ram.co.uk]
Look out for the sand taking the front wheel away from your line.  
Weight slightly forward to keep the steering line straight.  Look out 
for hitting this stuff too fast and burying the front wheel - instant 
faceplant.  Really sandy trails can tire you really fast - they are 
easier in damp than dry conditions.
Riding in sand is much like riding in mud or snow.

Doug van Houten (?):
Keep the front end light and grind away with low gearing.
If the front end is to heavy, the front tire will sink and you will endo.
Good places for riding in sand are on lake beaches, river shores, or sand
volleyball pits.
In Wyoming, we don't have too much sand either, but do have enough so
I know how to ride it.

[rokslyde@sowebo.charm.net]
Sand is a very difficult substance to ride on.  Once you get started 
it is best not to stop.  Turning on sand is no easy trick.  Take the 
turn VERY gradually and do NOT lean.  Leaning will simply make you 
fall over.  Turning sharp doesn't work either, your front tire will 
simply plow the sand until you stop (or fall).

Sand has the same effect as sandpaper on bikes.  It grinds and wears 
parts very quickly.  Do not ride a bike you like on the beach.

J. Wesley Prince [wesprince@csra.net] 
I have many hours of experience in the infamous Moab sand pits and have read
a few mag articles on the subject.

Sand Riding:
1. The bigger the meat (tire carcass) the better the ride when it comes to
sand. 
2. Have a positive attitude (helps in all technical scenarios).
3. Carry as much momentum (speed) into the pit as possible.  Try to maintain
this momentum as best you can.
4. Shift down a gear or 2 to prevent bog down.  It generally doesn't help to
stand.
5. Get the weight on the back wheel and let the front tire float a bit.
6. DO NOT attempt to hold a straight line by steering.  The front wheel will
only dig in and bury you.  Allow the front wheel to drift around a bit.  Keep
a light touch on the steering.  If you are starting to worry about your line,
you can try a combo of light steering and weight shifting (one side or the
other) to correct.  Sometimes you will start to drift way off line and will
need to steer to stay on the path.  Try to start early and maintain a smooth
arc.  A quick move will likely fail.
7. Use a smooth spin.  Power stroking will only break the rear wheel and slow
your momentum.
8. If you ride in a sand infested area, consider going to wax for your lube.
The sand will stick to the oil and grind away at your drivetrain.

Rik Allen [richard@prl.research.philips.com]
Snow is similar, but slippier. Stay light on the bike if you can - an
even weight will help prevent bedding in too badly.

Short stretches you can skim over if you hit them fast with the weight
at the back. Weight too far back tough and when the back wheel slows
down as it digs in, your weight will go forward, the front wheel will
dig in, and over the bars you go. Be careful.