Rating is only one part of prioritizing requirements but you need to select an appropriate technique
Voting can be done through a pre-session survey or in-session. Key success factors include:
1) Setup – the right needs and requirements to be prioritized are chosen (purpose based)
2) Involvement – the right stakeholders are involved in prioritization
3) Facilitation – a skilled facilitator is used
4) Tools – the right methods and tools for voting are used
Here are the four main rating techniques for prioritizing requirements