It's pretty simple.
The most important thing is to set up an alternative email account. Several years ago, I set up an email account called firstname.lastname@example.org. I did that because a lot of web sites required an email account. Yes, I know there's a little box on the e-form that says "If you would like to get offers...." that you can click to prevent getting unsolicited emails, but even that doesn't guarantee that you won't get offers. Thus, the alternative email account.
If you go to a trade show, it's a good idea to use that alternative email account when registering. A lot of trade shows captured your email when you visit their booth by zapping your badge with their ray guns. If you really wanted to get information from a vendor, you'll give them a business card with your email and contact numbers.
Also, if you send out a press release to someone, it's best to use a matt (at) gmail (dot) com address instead of the email@example.com tag. And, as I have learned from sending out Business Wire news releases, the use of (two-one-zero) instead of 210. Both of these simple techniques help lower the possibility that some sales professional will call me with the offer of a lifetime.
And, then there are the well meaning relatives and friends who want to send you their jokes and chain letters. How can I tell my Uncle Bill, the guy who used to change my diapers as a kid, that I don't want to get his missives?
Would he respond well to an email like: "Dear Uncle, I am trying to help the world save energy. As I don't really read all of your jokes, could you hold back on those jokes so I can help lower my energy costs?"
Or what about: "My Internet account is monitoring my bandwidth usage. Your jokes are costing me money...."
So, yes, I'll continue as an Internet energy waster. It's the courteous thing to do.