[Yukon Jack]

If possible I much prefer to be able to work on end of the vehicle at a time. That way I have one axle with tires supporting the truck, then I can place the jack stands like grendel says, more to the center or a little back from center of the vehicle and I feel pretty safe under there.

Like Mudder said, never use concrete blocks. I have seen them crumble under the weight of a truck. Yes they are strong, yes they are for buildings, no they aren't for holding up a truck.

Always give the vehicle a good push or two when you have it on jack stands to assure yourself that everything is laying secure. Some people will lay stacked tires seated on rims near their jack location as an extra bit of security.

What ever you do, you can't have overkill when supporting a vehicle.