1) Read the requirement 1-3 times
2) Understand the message in them
3) Identify the Business Rules, constraints, Flow, Navigation, Dependencies
4) Refer mock-ups, related documents(could be from external systems)
5) Communicate the GAP(clarifications, doubts, thoughts or ideas)
6) Derive the functional points
When we first get the requirement from client, they will be just an overview type so we do some meetings with them and try to get detailed requirements via discussion with client and then with our development team. After this, we refer to the existing system if there is any and will try to get some more detailed idea about requirements. Then we prepare requirements understanding document and send that to client. Client will go through that and will either approve that or will give their ideas or suggestions about the requirement mentioned in the document. We continue this cycle until the document is final. Then we prepare SRS and send that to client for confirmation. Once this is confirmed then we prepare test cases on the basis of the SRS.
Let me know if you have any queries regarding this process. And also correct me if I am wrong on something here.