Have you noticed that 'lessons learned' sessions are often a round of high fives or blame and recrimination at the end of a project, rather than a dynamic tool to build project success? A lessons learned session is when the project team and key stakeholders review what has gone well and poorly in a project, builds a clear understanding of why and uses that to come up with lessons (advice for a similar situation to get an better outcome) and discrete actions (to improve the normal way of doing things). The idea is that you both build on what has been done well and learn from what has gone wrong to get better results.
Don't wait until the end!
I cannot stress this enough. Lessons learned sessions at the end of a project can be helpful for the organisation (particularly if it regularly undertakes projects) but the best way for it to make difference for that project is to hold them earlier on, for instance at key stage gates and when the project is transitioning from development to delivery. You'll have an opportunity to identify risks, which you can incorporate in the risk management action plan. You should review lessons learned from other similar projects at the start of a new project, to make sure you truly learn from what's come before (and didn't merely record it).
In addition to those factors, you'll often find that the team are moving on to other projects and some snagging may be left to the operational department. It can be difficult to get hold of the informed stakeholders you need to get the most out of the workshop and subsequent follow up.
Make lessons accessible
In order to prevent your work from going to waste, you need a corporate retention system that is better than filing lessons away, never to be seen again, and certainly not learnt. Make lessons accessible by utilising metadata in your system to 'tag' files with key words, so they are searchable. This doesn't have to be complex: SharePoint, Evernote and many systems that store files and metadata can be used for this purpose. Jive has been purposefully designed to enable collaboration and knowledge sharing in organisations.
Actions need to drive meaningful change
This can be big, requiring an organisational process change or small, but either way, you need to ensure someone within the room gets an action that will change something within the business.
The aviation industry is excellent at this: incidents are rigorously studied to understand why they occurred and then, if appropriate, procedures are changed on an international scale. Taking this so seriously is one of the reasons why aviation is one of the safest forms of travel and also why their regulations are said to be 'written in blood'.
When done correctly, lessons learned exercises are a powerful tool for improving the efficacy and efficiency of projects and programmes and can have far reaching implications. They can take anecdotal knowledge from the team and turn it into corporate knowledge that enriches your organisation and leaves a legacy when the team has moved on. Make the most of lessons learned sessions to avoid the 'too little, too late' syndrome.