For an electric heater - very little
On an annual basis perhaps give it a clean. Turn off the power and use a duster or damp cloth to clean the reflector behind the lamp. This will ensure the heater is operating at peak efficiency.
Gas heaters on the other hand DO NEED Regular checking.
Every time you change the gas bottle check the hose fitting to the regulator is really secure, the hose butts right up to the regulator and the jubilee clip is tight (do the same check at the other end where the hose is connected to the heater). Also check that the regulators fitting to the gas bottle is really secure with no detectable movement between the regulator and bottle.
In addition to the above, we recommend that on a regular basis you give the hose a “Soap Test” – Put some soapy water into a spray bottle and spray every part of the hose looking for any bubbles that would indicate a gas leak. If you find a leak, change the hose immediately.