They'll be trying to decide if they can make a deal work with you.
Be honest, be prepared to decline to provide proprietary information (some are fishing for this to build clones of you), and treat the call like a prelude to either cashing out or getting fleeced.
Check that VC's background at thefunded.com, and take stock of yourself. Build yourself a "gut-check" spreadsheet table of amount invested in you vs. percentage taken. They may want to invest more than you want to take. Figure out where on that table your sweet spot is, and bear in mind that depending on how well your company is doing, that the sweet spot might have zero size.
Develop yourself a strategy of if you're going to approach other VC's with an offer you get. Others may be willing to value you higher or offer better terms if you can shop your term sheet around. You may not feel comfortable doing that, but be certain internally what's on the table.
In the end, remember: no deal is too good to walk away from.
