Sending your kid off to college was probably pretty hard at first. Those first few weeks that they're gone, all you can think about is what they're doing; if they're eating right, if they're keeping up with their school work, if they're getting enough sleep, but what you should be thinking about is what you can do with their empty bedroom.
Now, you can't just go diving in and getting rid of everything that your kid has accumulated over the years. There will be things that they want to keep, things that you can't bear to let go of, and everything else. It will be impossible for you to know what's what for sure, but you don't really have to. You can clear that room out without difficulty—except for having to go through the scary stuff that's been hiding under the bed for the last ten years.
You want to keep things as organized as possible. This is because if your kid is like most, you will have a very hard time talking them into going through the stuff after it's in storage.
Get a few different colored bins; one color for the stuff that you know they'd want to keep, one for the stuff that you won't let go of, and one for the things that you aren't quite sure what they'd want you to do with it.
As you pack, take pictures of things as you put them in the bins. You can then number the bins and keep an inventory of what you have for your kid to go through. You can send a digital file to your kid so that they can look through everything at that moment if you'd like. This way, you can eliminate the things that they know they don't want and reduce the load that needs to be taken to storage.
Protect things in Storage
Now, find a unit storage service that is nearby your home, or at least, convenient for you to get to. Before you go unloading your car, you will need to put something down on the floor to keep it up off of the concrete. Simple wooden pallets can be picked up for cheap or free and will keep things off of the ground and dry.
There's no guarantee that your kid won't boomerang back after their time at college, but the good part about keeping all of their stuff in storage is that they'll have it when they come back to you, regardless of whether it's to stay or visit.