3 key pillars of sustainable design/development

The three key pillars of sustainability are:

Social - people
Environmental - planet
Economic - profit

The word 'pillar' suggests separate, static entities when in fact there is a dynamic between all three elements. It might be easier to think of them as three balls in a juggling act - the trick is to keep them working together in a simple, smooth process. At the moment, it has to be said, we often don't juggle too well. But we're making progress.
http://www.design-council.org/About-Design/Business-Essentials/Sustainability/?print=true

Sustainability involves juggling a number of issues in a careful balancing act

Materials - using less material (lightweighting), fewer materials (making it easier to recycle) and if possible avoiding toxic substances and choosing renewable or recycled/recyclable.

Dematerialisation - could include some of the above, lightweighting for example, but also designing things to be multifunctional, or finding a different way to deliver the same benefit through a service or product-service combination, variously referred to as selling performance or results, or 'product service systems' (PSS).

Design for disassembly - making things easy to take apart so they can be repaired, serviced, upgraded, remanufactured, or recycled, such as through modular design, or smart materials which can self-disassemble when needed.

Energy - both in production (which would mean looking at the manufacturing process), and in use and disposal. This includes minimising energy use, moving to the use of renewable energy, and extracting energy from waste in some cases.

Life extension - keeping a product, or its parts or materials, in productive use for their optimal lifespan, so slowing or preventing the linear flow of materials from extraction and processing to disposal.

Transport - minimising it, that is. Sourcing a renewable, impeccably green material which you ship four times round the world may not be as sustainable as something a little less clean from down the road.

Nevertheless, a 'green product' could actually be unsustainable. Let's imagine you make something that uses recyclable and renewable materials, but you use child labour so nobody wants to buy it, and it ends up being dumped anyway, driving you out of business. You would have thrown the environmental ball up in the air for a moment, but you'd have dropped the social and economic balls, with the environmental one following soon after.
http://www.design-council.org/About-Design/Business-Essentials/Sustainability/Its-not-easy-being-green/