In my opinion....
While you do not want to leave any money on the table you
absolutely should have an idea of what you want for compensation before you interview.
That said, if this is something new that is different than what you have done in the past, it is possible you may not know what to ask for. But that is where your communication skills come into play. It never hurts if in question to ask what the typical compensation package consists of for this position. Most companies already know this before they interview but there's always wiggle room depending on each applicant's individual track record and what he brings to the table.
Lots of variables so I don't think you can put a template on every situation but again your communication skills will serve you well if you can use them wisely.
i keep thinking about the old saying - the first one who talks loses
The First Rule Of Negotiation: First One To Talk Loses | justinmchood.com