The answer to that question determines how much (if any) mapping of Current State you need to do. Certified Process Masters (www.certifiedprocessprofessional.com ) will tell you the answer is only enough to know what you need to change it to, as within non manufacturing processes the actual process we depict does not physically exist. It is a collective hallucination.
So start with the most simple and accessible techniques (Post-It notes and whitepaper) then apply what you need to achieve the successful customer outcome. A subsequent question then arises - how do you know what is applicable? Run the sponsor/stakeholders through the SCO Map, and that will develop for you the discrete and measureable deliverables to determine the 'best' approach (it takes about 60 minutes to do that).
Everything should be targeted towards making customers lives (internal and external) easier, simpler and more successful.
If you haven't yet been introduced to the SCO map concept here's an overview http://bit.ly/SCOmap