I'll add a slightly different take: know your audience. We get so many people contacting us assuming they have something we need, when in fact it's not even remotely relevant. It's a total time waster and really annoying.

Do a little research ahead of time and find out if the company is even in a position to want your perk. And each time you find a happy customer, ask them for the name of 3 other folks worth contacting...