There are a number of questions and comments that might apply. The first one is: Do your homework and some due diligence. Learn all you can about them.
I assume you mean these are firms that manage & invest other peoples money.
If you`re personally dealing with VCs, always be mindful of what terms of ownership they want. Many small business owners have avoided reading the fine legal print and did not realize exactly how much control they gave to the VC until it was too late. To be clear, firms that engage in sell-offs or hostile takeovers are a minority. VCs are definitely not the bad guys and are a great "next step". But there is only one of you and a multitude of VC firms, so you can afford to look around for the most favorable terms.
Knowing who owns and runs the VC firm can often be a good predictor of their investment philosophy and how much leeway they give the companies they invest in before they decide to liquidate their stakes.
I have deal with VC`s before and let me give you a little advice that will hopefully help you. VC`s are different from during the dot com boom (bust) Most VC`s nowadays want to see cash flow upfront and see that you are well on your way to becoming successful. Gone are the days when VC`s just throw money at an idea. Most VC`s want a "working model" to initially invest in with a first round of financing. Then once revenues grow, they are generally open to a second round of financing. There is also another twist here. Most of the time now VC`s want to have an exit strategy after the second round. This generally, but not always consists of buying you and your partners out or to broker a deal with an interested buyer. Many VC`s will now utilize "forensic accountants" to go thru every detail of your cash flow. Depending on your level of revenue and stage of startup development, you might wish to contact Austin Ventures in Austin Texas and pitch your idea to them. They have very deep pockets and work well with their clients.. Don`t expect to do an "elevator pitch" with folks at this level though, they play hardball and are extremely successful at what they do.
Hope this helps and if i can be of any future help please don`t hesitate to contact me at email@example.com