I've had best results when adding honey once fermentation has slowed down. So after ~2-3 weeks in primary, add X pounds of honey to the batch. I would start off with a lower amount than you might be thinking about, let it ferment out, give it a little more time, then taste it. IF you need more, repeat the process. I also had some good results carbonating those same batches with honey.
Since those days, I've switched to using honey malt in my mash when I want honey flavor/character in batches. It doesn't thin the brew out any, and adds a honey flavor to it. Basically, you get the best of both worlds. BUT, if you want to add the flavors of a particular type of honey, you'll need to use that honey.
IF you want to add it before you pitch the yeast, it's best (IMO/IME) to add it during the cool-down of the wort. Once you've dipped below 110-100F, it's safe to add honey. Safe in that you won't lose what flavors the honey has to offer the brew. Heat it too far, and you'll lose too much. IF you feel you simply must heat it up to 'make it safe' (a 100% unnecessary step), then don't go above 140-150F. If you do, only do it for a few seconds. Any longer and you'll lose the goodness the honey can offer you. If you add it to the boil, you might as well just pour sugar into the brew. Since that's about all you'll get from the honey. IMO, that's a waste of good honey.
There's a reason why the majority of experienced mazers don't heat their honey at all when making mead.