I know it might seem strange to talk about coming home before anything else, but it makes sense. Just bear with me, please.
Two of the key components to reducing re-entry shock are Time and Organization, and they go hand-in-hand. You need time to get organized, and being organized will save you time.
When I returned to the US, I had about a week to find an apartment, move into that apartment, find a job, and get ready for the semester to begin. I got it done, but 8 weeks later, I still haven't finished unpacking. Nor did I have time to reflect on what I'd been through.
So my first bit of advice would be to give yourself plenty of time to adjust before you really have start back to work/school/whatever. Take stock of what you'll be returning to: Where will you be staying? Will you have/need a car? Where will you be working? I had to make several snap judgments and quick decisions. Although I really don't regret anything, I do wish I'd had more time to consider all my options.
I also wish I'd given myself more time to get packed before I left the US. I worked up until the week before I left, and again, I should have given myself at least another week. Wound up just throwing things in boxes. Stuff got labeled, but I should have divided things up differently.
The second bit of advice is to give yourself time to get packed, to be the one doing the packing, and to be the one doing the storing. This will help you when you return--you'll know where everything is, so you can get to those things that you need most immediately. I was lucky enough to have people put away and store my stuff for me, but there are a few things I still haven't found.
A couple quick tips:
---Pack clothes away by season and function. If you return in the middle of summer, you're going to need shorts and t-shirts, not sweaters and coats.
---Label everything. "Kitchen" is too broad - you should be able to know what's in a box without opening it. This is also useful for people back home if you need something sent to you.
---Collect boxes whenever you can and store them flattened if possible. If you have the money, go ahead and buy nice sotrage boxes. Keep an eye out for sales. This is more costly, but they will stack better and will be easier to label.
---Consider investing in large, re-usable plastic tubs. If you're like me and move every year, it might be worth it to have an "office" tub, a "dish" tub, a "hardware" tub.
---Take you clothes to the cleaners and ask them to be folded instead of put on hangers. This means one less thing for you to worry about, makes storage easier since they're already folded, and if stored well, they'll be ready to wear right out of storage.