COMMOM SENSE.....
Watch the surface your on whether using jack stands or ramps. Absolutely NO concrete blocks.
The right tool for the job (ramps or stands)
...maybe a friend to hang out with you while under the truck (he can hand you wrenches)
Even with the best precautions I personally like to keep a jack with just a little pressure, either under the front, back or side just for "insurance"
.....perhaps its because my dad had a IHC pickup fall and crush him breaking 13 ribs. He lived but barely.
Sage advice as always Alvin,I actually lost a friend in similar circumstances,a shop buddy/friend is invaluable.
If Brian had someone there he would've survived the crush injuries,what got him was he suffocated,everytime he exhaled he couldn't breath back in due to the weight on him.......
If i'm under mine it's always on 4 3ton jackstands and i'm well within earshot of the house should anything happen.