For those of you who have (or are creating) a sustainable software development strategy, how did your organization decide to prioritize this, and what challenges are the main challenges you’re currently having to overcome?

We are trying always to focus in design process of applications on 3 main aspects:

- energy consumption: correct resource allocation, scale up/down, metrics, alarms on budget consumptions, periodical review of metrics
- code only what is needed in order to keep under control TCO: more large is your codebase more cost and complexity you have in maintenance
- focus on code quality, security, privacy and performance because a good application improve the quality of life of people and has a good impact on the sustainability

Sorry, I am not very clear on the terminology used. Does "sustainable" mean the process is sustainable to repeat and support within the organization, or is it sustainable for the environment and energy efficiency?
For the first definition, we are adopting Agile and DevOps methodologies and tools.
For the second definition, it has not been prioritized for the internal software development strategy, however we look for sustainability factors and metrics in our vendor/COTS portfolio. Specifically, selecting colo-DCs and telecom facilities is driven by vendor's ability to be sustainable and have plans to minimize their carbon footprint. 

This is a work in progress in practicing a sensible sustainable software development strategy, in order to contribute to economic growth, do good for the environment and promote/improve social progress. The biggest challenges we face are poor coding standards and lack of green software development knowledge.