Start with the usual. Unplug fuel pump(power to it), spray some easy start and check whether it fires up for a second or two. If it does - you have spark but something wrong with the fuel. If it doesn't - you have something wrong with the spark. Might be lot of things, from CPS through amplifier to pump or injector issues. We need more info
1997, 4.0 LWB X300 - Unlucky car but still a daily driver.
1988, 3.6S XJS - Never ending restoration project.
1994, 3.2S X300 - Accident damaged, October 2015. Gone!
1994, 3.2S XJ40 - Long gone.