What laws should I be aware of as a motorcyclist going from the UK to Germany via the Netherlands

In terms of law there isn't much really. Most traffic/vehicle laws have been normalized across the EU specifically to make this easy. So in general, if comply with rules in the UK you comply with the rules across the EU.

A UK license is valid in the whole of the EU, insurance of your vehicle is legally required to cover at least third-party damage across the whole of the EU. (You may want to check your policy to see if there is any additional coverage which is limited to the just the UK). Your vehicle needs to be safe and road worthy, if it passed UK MOT that should be fine but you might want to take the along the papers to prove that. Noise regulations are the same throughout the EU as well.

What is left is abiding by the local traffic laws, so get a grip on dealing with speed limits and distance in kilometers instead of miles and remember to drive on the correct side of the road. Otherwise, if you pay attention to the road signs and apply common sense you will be fine.

Some things that might be relevant:

• It is allowed to pass between lanes in standing or slow moving traffic but only at a low speed difference (max 10KM/h) and never using the hard shoulder.
• Speeds indicated on electronic signs above the road are limits, even when there isn't a red border around them.
• A green arrow or red cross on overhead signs trumps the lines on the road. You'll come a cross places where this is relevant. (See How should you drive on rush-hour lanes ("Spitsstrook") in the Netherlands if they are open?)

The 'Going Abroad' Site/App also provides a nice overview of basic traffic rules in all EU countries.

For Germany:

• We drive on the opposite side of the road, as you hopefully already know.
• The default speed limits are 50 km/h in built up areas, and 100 km/h outside of built up areas. There is no speed limit on the Autobahn unless indicated.
• The speed cameras look are either a metal box on a pole, or a thick grey pole filled with cameras. Not all of them seem to catch motorcycles as they have no front plates (the poles are more likely to take a picture from the front and the back). If you see a bright red flash, you've been caught speeding, but that doesn't mean you'll get a fine.
• The Autobahn is the least interesting way to ride through the country. I highly suggest turning off highways and enjoying the nice country roads. Use a relief map to find pleasant mountain roads.