I don't know if what I did is what HTC expects, but when I received the phone, I plugged it in immediately. I then turned it on a few seconds later. I left the phone plugged in for maybe 6-7 hours before unplugging it. I did, however, activate it and use it a bit while plugged in.
After the first use, I let the phone die out most of the way before fully charging again, but this time for more like 3-4 hours.
Since then I've never not fully charged the phone (meaning the light turns green -- usually 90-120 minutes). Can't say whether this has helped, but I've had great battery life.
My battery life has been excellent for the month I've had the phone. I get around 24-30 hours (sometimes even more) in before I hit yellow on the battery indicator.