I've been platinum for around 5 years now, and I almost never request a complimentary upgrade when I business travel.

What are the best practices for requesting and successfully getting complimentary upgrades?

I've called a week in advance before to request a complimentary upgrade, and they say to call closer.

I've tried to do an early check-in, and they said if I wait they can give me an upgrade (without me requesting). In fact I've had more complimentary upgrades when I DIDN'T ask for it, than when I did.

What can I do to maximize my chances? Is there a time range before the stay which is optimal to request these things? Is calling the best way to do it?