Be careful when lowering the van onto stands - if using a trolley jack then the van can often move away from the stands as it is lowered. Take time to lower the van slowly until it is 'just' about to settle on the stands and then re-align the stands to make sure they are correctly located.
Lower slowly onto the stands, but leave the jack in place about 5mm clear of support (not actually supporting). Now from the side/front shake/push the van in all directions with 'reasonable' force to make sure the van is stable and secure on the stands. This is vital because you want to make sure that the van won't fall off the stands when working under it. You'll be amazed how much force you put through when undoing bolts/removing wheels etc....so making the stands 100% stable is pretty critical.
Where possible leave the jack in place as a 'back-up' and also leave the wheels on as much as possible if working under the motor. That way, if the stands give way....AND the jack....then you'll still have some clearance under the vehicle.
I don't want to put the frighteners up you.....and I hope you don't think I'm teaching you to suck eggs or anything, but you can't put a price on safety when working under a motor.
There are lots of other tips and advice about jacking/supporting and working under vehicles, but use your common sense and you should be OK
