How do I tackle that difficult conversation?

We all know that difficult topics can make for difficult conversations... and the results can be pretty disastrous. How do we make that easier? How do we make sure that we give ourselves the best chance of a productive chat, where everyone feels better at the end and you can actually resolve an issue... or at least make some headway?

When's the best time to tackle something tricky? Is it when we feel like our blood is boiling and we can't rest until we sort something (or somebody!) out? Would we train our dog in that state of mind?