Check that there is adequate ventilation around your boiler. If your boiler is located in a cupboard, keep the area around it clear of clutter.
Check that all external vents, flues and air bricks are clear.
If you can see the pilot light in your boiler, make sure that it has a strong blue flame (if you have a gas boiler). If the flame is yellow or smoky you should report the problem to an engineer immediately.
Flush your boiler twice a year with clean water. You may also want to consider using a descaler.
If you have an oil boiler, check your oil levels regularly. If you run out of oil, your system may suck sludge and debris from the bottom of the tank into the pipes, damaging your boiler.
Keep a copy of your boiler manual close to hand. If you do not have a copy of your manual, contact the manufacturer or check their website.
Make sure that you have a Carbon Monoxide detector installed in the same room as your boiler and test it at least once a month.