Hello

Don't sell your house, quit your job and go on a multi year RTW if you haven't done smaller trips already.
A RTW is nothing different than several trips stringed together.
Big difference is, after some months, travelling becomes your life, it gets less exiting, you have to deal with that.

What I would give as advice to beginners based on my experiences, in order of importance to me:

whatever:
-vaccinations, I went as far as rabies.
-insurances, medical and transport home (you, not the bike)
-liability for the bike, as far as possible, huge pain in the ass to get, but worse if you need it and don't have it.
-someone who can go to the bank for you at home and all that stuff.
-a lot more like that...

language:
Important, but you can't learn all of them. To me that meant, first I had to learn english.
Depends also on how long you are in a region and how alien a language is to your native tongue.
At first, english natives have a huge advantage, but hard to deny to understand english if need, I can speak to someone in my native tongue and they will understand that I can't speak english (corrupt cops, etc.).

first aid:
Difficult, I have more or less every 10 years a first-aid course, the one that you need for the driving permit. They are basically meant to help until the rescuers arrive. How much does it help me as a solo rider?
It may open ones eyes on how fragile the body is and why you should do everything to prevent an injury.

on road:
-learn to read the road and the traffic and the surrounding area.
In places where live takes place on the street up to 10m away from the road on both sides.

off road:
(Warning, the following might be seen by some as blasphemy, especially in internet forums! So, if you are sensitive to that, stop reading and just skip it.)
If you go for a training, take one where they teach how YOU can ride your bike with YOUR full travel setup on the road surfaces that you will encounter on your RTW, by someone who has done it by themselves.
Don't know where you can find that.
A training on an empty (no luggagues) light bike is, to me, useless.
Learn your limits, turn around when it gets to tough for you.
Most important, learn to ride without falling, every fall is an accident, not part of the trip.
Keep in mind where the next hospital is and how or by whom you might get there.

sushi

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My RTW:
http://www.youtube.com/user/MrXt660ztenere