Some good advice above
Prep the bike as said.
Tyres must be up to it, at leats 1/2 left before you start, otherwise fit new before you set off.
Change the oil+filter, it's just a good precaution. Don't be tempted to overfill it "in case it uses some". Just set it near the max. Oil is available abroad!
If the clutch cable is at all suspect, fit a new one. It's nicer with a new one and it's only a tenner or so.
Definitely fit a Scottoiler if you haven't already. Do it a few weeks before hand so you can check the settings etc.
Don't set the chain too tight!
Check coolant.
Check brakes.
Check the charging and battery are OK. The reg/rectifiers aren't the most reliable.
Make sure you do all this a couple of weeks in advance so you are 100% sure it's all OK before setting off.
Make absolutely sure luggage is secure. Avoid loose single bungees (can drop into wheel if they come unhooked). Fix bungees together with cable ties or knot them together.
It will rain. Make sure your waterproofs are effective!
Fit a fender extender if you haven't already. Riding an Autobahn in pouring rain on one cylinder ain't fun.
Apply some silicone grease (or red rubber grease) to the front plug cap boot.
Get bike insurance cover extended for continental use if necessary (std. cover is "legal minimum" only usually).
Get personal travel insurance. Consider annual policy (around £50 or 60 typ) if you might use it again. Make
absolutely sure it covers you for riding a bike. I use the Post Office, but lots of competition so shop around.
Make sure you have the new "credit card" type E111 (from Post Office), the older type paper ones aren't valid.
MCN usually gets you some discount on ferries.
I've found some really cheap B&B's in small villages just off Autobahns in Germany, usually set up for business travellers. No real need to book in advance. Don't leave finding your overnight stop too late, I like to find somewhere around 5pm, gives you a couple of hours margin for error.
Don't run out of fuel! If in doubt, top up! Trust me.
You must have spare specs if you wear them.
Take care, some drivers are nutters (e.g. Brussels). On Autobahns, watch mirrors for Mercs/BMW/Posches approaching at 150mph!
Keep to the inside lane where possible, lane discipline is much better on the continent. Laws still apply to you.
Have fun
