Some more things to consider:

Look ahead and plan your route, don't just look immediately in front of the bike.

Shift your weight around on the bike to help balance and steer. Move your back side and body forwards when going uphill and backwards when going downhill. When going through soft sand keeping the weight back and off the front will help the front tyre "glide" over and not dig in.
Shifting weight from foot to foot will help you steer the bike with little input from the bars. It will also help maintain grip on side slope - have more weight on the uphill footpeg and it will help the tyres grip and not slide down the slope.

Practice your brake control on nice flat gravelly surface. Get to know how to control the bike to a stop with the back wheel locked and get a feel for a front wheel slide by momentarily locking the front whilst keeping drive to rear. These skill will help lessen panic when your are on a hill and the brakes lock up with a little too much pressure applied or a rapid change in surface under the trye.

Above all...don't be a passenger!!!!
Too many people are stiff and rigid and do not not move and flow with the bikes movements. If you are standing stiffly then you will not be able to control the bike. I often think of the bike as a "sloppy link" between me and the ground, you must allow it to be able to pitch, roll and yaw underneath you while maintaining control of the whole thing.

The best thing I ever did was go on a BMW Offroad skills course and learnt an amazing amount in one weekend. Not cheap but I still think it was money very well spent. Other training courses are available ;o)

Have fun out there!

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2011 XT660Z, in BLACK of course!
Mods done:
Lost the will to keep track!