Even if you are a regular rider on the continent, it still pays to take things easy and concentrate even harder for the first few miles as you will be on the 'wrong' side of the road. You will need to adjust to a different pace and styles of driving to the one you are used to, as well as varying speed limits that are different to the UK. Remember speeds will be shown in kph and you will need to focus on the smaller print on your speedo unless it is electronic and can be switched across to kph.
It is a good idea to try and use a motorway or similar road to take you out of port to give you time to settle down and 're-calibrate' your brain to the general 'keep right' principle of riding on the continent. A useful tip is always to use fuel stations on your own side of the road and not cross to the opposite carriageway. If you do, be particularly careful when leaving as this simple act is often when people forget which side of the road they should be on! Hopefully you will have planned your journey beforehand with reasonable mileages and stops. If you are travelling alone you can set your own pace, but group riding involves a bit more thought.
Depending on the size, it may be best to agree regular meeting points so people can ride at their own pace and not feel pressurised to keep up. All should have the final destination and telephone numbers of the group. If you want to keep together then the golden rule is to ride at the pace of the slowest rider and not the fastest so as not to sour the group dynamic. The idea is to have fun! Always be careful where you park, not only in respect of local parking regulations, but also for security. Consider some form of basic additional security like a disc lock to use especially when the bike is parked out of sight at night
Finally it pays to study the traffic regulations and signs applicable to the country you are in. If in doubt the European police website has some driving guides which should help keep you within the law as will keeping your headlight on at all times and staying within the posted speed limits!
Always remember when riding on the continent, think right, look left!