Brake pads should be inspected every 6,000 miles (10,000 km) or any time the wheels are off for rotation or other servicing. Pads should be replaced if 1/8" or less of lining material is left. Front pads are easy to inspect with the wheels off but rear pads, due to the inboard brake location, can be easily inspected only if the car is elevated. Inspection should also include checking the condition of caliper piston seals and flexible brake hoses. You'll want to check for splits, cracking, or any sign of deterioration. Any sign of fluid leakage is cause for immediate remedial action.
When checking rear brakes is it important to check for leakage of the rear axle seals. If they are leaking badly, gear oil from the differential will be slung onto the brakes. If the seals are leaking just slightly, their replacement (big job!) can be postponed by religious cleaning of the area with aerosol brake cleaner on a regular basis to keep the leakage from migrating onto the brakes.
Brake fluid level in the master cylinder should be checked anytime you have the bonnet (hood) lifted for servicing, but not less than once a month. You'll want to check for external fluid leaks and overall appearance and condition. It is normal to add fluid from time-to-time as the brake pads wear down; as the pads wear the caliper pistons move outward and create more space for fluid to occupy.
The brake fluid should be completely flushed through and replaced by fresh fluid every 18 months, according to the Jaguar service manual. This important service is often overlooked. Old, dirty fluid boils at a lower temperature and can be the cause of brake fade and/or soft brake pedal feel.
The brake fluid of choice among most Jag owners is Castrol GT/LMA. Ask your local parts supply to get some for you if they don't carry it - most do, however. Some Jag owners prefer synthetic brake fluid. See the Jaguar Forums for hours of discussion on the subject. Generally speaking the synthetic fluid works very well providing all traces of regular fluid have been removed from the system.
Brake hoses should be replaced at the first sign of deterioration, or at a minimum every 10 years.
Brake rotors require no regular service but will often warp due to age and heat, giving a pulsating feel to the pedal during braking. New rotors are readily available and inexpensive so considering the labor involved, it usually makes sense to replace them rather than having them resurfaced.
The vacuum hose and piping to the power brake servo should be checked for cracking, softeness, or general deterioration at every oil change.
The best maintenence for your parking brake is to use it daily. Lack of use will make the calipers seize up and render the parking brakes inoperative. The small pads for the parking brakes almost never need replacement.
If the brake pads need replacing you'll be amazed at the variety of pads to select from. See the Jaguar Forums for discussion but it is generally accepted that OEM pads or equivalent are prefered. High performance pads and/or pads with a very high metallic contact require higher pedal pressure and accelerate rotor wear.