Get a combined alarm and electronic immobiliser fitted professionally. Thatcham and Sold Secure recommend some of the best and your insurance company may give you a discount on your premiums.
Get a good disc lock or better still, a U-lock - make sure it's long enough.
Secure your bike to something solid that can't be moved and keep the lock off the ground - this makes it harder to break.
Put obvious security markings on as many parts of your bike as possible, using the Vehicle Identification Number (VIN), the registration number or your postcode linked to a recognised database.
If you've got a garage use it and lock it. If not, ground anchors are a good bet and cover your bike if you can.
Keep you keys safe and out of sight at all times.
Always put the steering lock on.
Don't leave your helmet or other possessions on the bike.
If you ride an off-road bike, ask the DVLA to register its details (frame and engine numbers) on their own and police computers - it's free.
If you're buying a second hand bike or parts, be wary of 'bargains'. Have a good look at the registration documents and check the bike's history with HPI Group Ltd, the AA or the RAC