A task with performance engineering that’s often encountered is to define requirements for performance. This is a task that isn’t easy to accomplish, especially if you start from scratch. On the SearchSoftwareQuality-Blog, a helpful article has been posted: Seven quick tips for better performance requirements.
It sums up the basics to get you started. The headlines of the tips aren’t that new for requirement engineering (“communicate with stakeholders”) – but the examples they give are quite useful, although not really new (like using quantiles/percentiles for response time limits).