One of the better tips I've seen before is when someone forwards you an email to transfer an action to you or just an introduction email, when you reply move that person to the BCC line, that way they see that you've taken over the thread but don't end up being copied into the entire ongoing debate:
Eg:
To: Sam
CC: Bob
From: Alice
Subject: TPS Reports Team Introduction.
Hi Sam, I'd like to introduce you to Bob, can you work with him on the TPS reports
----------------------
To:Bob
From: Sam
BCC: Alice
Subject: Re: TPS Reports Team Introduction.
(Thanks Alice, moving you to BCC)
Hi Bob, nice to meet you, where do we go next?
----------------------
From: Bob
To: Sam
Subject: Re: TPS Reports Team Introduction.
Blah, Blah Blah, Ponies