Invest in Additional Car Security
Any extra security measures you take to deter thieves from stealing your car will further decrease the risks you pose to the insurance company. For example, just by installing a Thatcham approved alarm can often save you up to 10% on your car insurance. You will normally be expected to have them fitted by professionals, as insurance companies might not take DIY fitted devices into account, even if they are Thatcham approved.
Immobilisers and steering locks also play a vital role in deterring the car thief, so by having these you are also lessening the overall risk that you pose to the insurance company.