How do I avoid having to bleed my radiator regularly?

If your radiator is cold at the top, then this is usually an indication that it needs bleeding.  Why set yourself up to have to do this time and again, when you can install an automatic bleed valve which will bleed your radiator for you without you having to lift a finger!

Automatic Radiator Bleed Valve

Of course, if you're constantly having to bleed your radiators, it would be advisable for you to call in the professionals, as it may be that there is an underlying cause that needs attention.  You should only need to bleed your radiators once or twice a year.