I agree with Don's approaches of clarifying both the email subject and who you are asking to do what. Some folks get hundreds of emails a day, so I think you are most likely to get your message across if it's clear in the first few lines; your prime real estate here is the email subject and the first few lines of the email body.
For Don's system in which the Cc: field denotes "FYI", those people receiving such an email need to be aware that this is the system, i.e. this is an implicit rather than an explicit message.
I know when I get an email I'm grateful when I can work out quickly and easily exactly what it is I'm supposed to do with it.
I don't have any real hard-and-fast rules for who goes in the to: and Cc: fields, but what I often do is make the first line of the email body look something like this:
Cc: Joe (ref. putting quote together), Bob (various next actions below), Karen/Chris/Katie (FYI)
If this is a little unprofessional or out of place for e.g. an email to a client, then you can send a second email to those additional people you're wanting to pass on explicit information to.