I think it's worth using a grounding strap, rather than touching a radiator. Touching a radiator will ground you
at that moment. You might build up enough of a charge to fry something afterwards. A grounding strap will keep you grounded.
You'll probably be fine touching a radiator only, but I think the extra protection of a grounding strap is worth a few quid.
If you do go on the radiator route, make sure that you touch an unpainted part. Any unpainted plumbing should do - it's a legal requirement that it be grounded. A radiator is just usually the most convenient thing.
And another reminder about the motherboard spacers, to keep it off the case (it will short through the case otherwise). That might well be the most common thing to overlook. Although I have seen one case that had bulbous mounting points and didn't use spacers.
Make sure you have plenty of time. It will probably take longer than you expect - it usually does.
Make sure that pets and small children can't bother you while you're building. They can easily fry or break stuff.
Read the motherboard manual. It'll all be in there.
Remember to say "Energise" a la Star Trek when you power up for the first time
