Here’s a quick one that has saved me time and helped me mask my frustration:
When dealing with a support agent via online chat, keep a copy of everything you type in a separate text file. That way when you think of a better way to explain yourself, or inevitably have to re-explain everything to another agent, you have text at the ready. It’s much less work to copy and paste the relevant bits than to write them all again, is less emotionally taxing, and you can look like the nice person you really are, even if this all has gone on far too long.