So, here's an assumption I make in my work pretty much all the time: if I want random people to change something (I work in behaviour change), I can't just lecture them on the benefits of a meat-free diet or taking shorter showers or whatever; I have to, somehow, ask them to first a) agree with me, and then b) agree to do it.
It's called 'making a commitment,' and I used to laugh but it totally works.
Erik at vegan.com made a post Animal Advocacy and The Power of Asking, and it reads like maybe he didn't know it! So I've put together a little reading list that's applicable to any activist, internet or otherwise, who is trying to make people change. I know this seems really formal and theoretical, but it's actually really applicable right down to the little things.
Commitment approaches to behaviour change can be seen in all sorts of things - buying a whatevercolorribbon is actually used as a commitment to the cause, and sometimes as a point of escalation (towards more action, more money, etc) by many charities and groups. And stakeholder commitment is considered an essential step to any organisational change, especially policy stuff.
Recommendations for behaviour change programs to reduce greenhouse impact in SA, a 2005 report written by the Conservation Council of SA. This is a broad overview of issues.
Quick Reference: Community-Based Social Marketing. CBSM is sort of the hip new thing that everyone is getting in to in behaviour change, and its premise is this: analyse people, educate people, normalise what you want them to do, then make them commit to it.
Community-Based Social Marketing as a Planning Tool, a 2002 thesis, chapters five and six in particular.
And one from outside the enviro/sustainability sphere:
Commitment to Change Instrument Enhances Program Planning, Implementation, and Evaluation, The Journal of Continuing Education in the Health Professions, 2004.
So it basically boils down to this: give them something specific to do. Then get them to say it, written or whatever. It helps.