Depending on the size, shape and volume of your van, you need to use all the space to your advantage wherever possible. Blankets and strong tie ups help you to accomplish this effectively.
Remember to try and use the full height of the van, turn things on their end like sofas, with a blanket or two for protection where needed. Tie other things to the wall that may tip or fall whilst being transported, like lamps or book cases. Stack lighter boxes on top of heavier ones to make a base layer you can build on top of.
Also make sure you have completely secured everything before you drive off to your new home.