Aussies and landing after jumps

One thing you can do is to make sure that your dog has the info on where he's going next just as he takes off to jump.  Directional training with body and voice cues.

 ditto what Spiritdogs said.  Give as much info ahead of time as you can so they are not trying to correct as they are landing, and that will help. Try not to do too many last minute changes of direction because that will cause him to land hard as he tries to figure out where he's going next instead of paying attention to his landing.

If you can, it would be good to give the directional info right before the dog jumps so that the dog can go into the jump knowing. Once the dog commits to the jump (generally a stride or two before it takes it), you can give your directional cue so the dog knows precisely how to jump.

You might also work on doing some jump grids. They are set up to specifically teach a dog how to collect, jump, and land properly.

I would work on training the dog to jump properly - not all dogs are naturally great jumpers but there are a lot of of things you can do to improve their skills. Some resources:

http://www.cleanrun.com/index.cfm?fuseaction=product.display&Product_ID=1457&ParentCat=171

http://www.cleanrun.com/index.cfm?fuseaction=product.display&Product_ID=177&ParentCat=171

 http://www.cleanrun.com/index.cfm?fuseaction=product.display&Product_ID=1499&ParentCat=171