Once the deliverables have been provided to the client, it is important to analyze how the project went. Often a questionnaire is given to the client for feedback. This questionnaire should be designed to obtain constructive feedback about the project: what went well (best practices), what didn't - what should we do more of, less of, and what should be avoided in the future. You should consider technology that was used and its effectiveness, how communication occurred and whether effective, how much the client was involved and whether this was adequate.
Design a short questionnaire. Use the template as an excellent example of a classic lessons learned document.