Imagine your company makes a new fitness tracking device and you want Ashton Kutcher to wear it, talk about it and promote your brand. The first thing you need to do, says Herb Karlitz, founder and president of the Manhattan-based luxury lifestyle and entertainment firm Karlitz & Company, is stop and ask yourself several questions.

Does the celebrity have any interest in your product or service?

Maybe you see someone like Ashton Kutcher as being an early adopter of technology, but if he doesn't exercise or care about fitness and health, it makes little sense to hire him to represent your fitness brand. "When partnering with a celebrity you have to make sure there's really an organic fit between the product and that person," Karlitz says. To figure out if there's a good match between the celebrity in question and your offering, just do some Internet research. The good news is the bigger the star, the more open their personal lives are to the public.

Who is the celebrity's publicist and how do I reach him or her?

Assuming you determine a particular celebrity may have an authentic interest in your product or service, track down his or her publicist--not an agent. Whereas it's a publicist's job to be intimately acquainted with everything about a celebrity's life so as to be prepared to pitch PR opportunities when they arise, an agent is mostly just interested in money. "It's about... for the right amount of money my client will represent your brand," Karlitz says. "And that's really not the right approach. It's about finding that right celebrity that really there's an organic fit. It's a home run if they actually use the product before you've even made that call." No luck reaching out to a publicist? If you're good at networking, chances are you know someone who knows someone who can help make a connection. If your network is lacking hire a firm to reach out for you.

Does the celebrity actually like your product or service?

It's one thing to pay Jennifer Aniston to wear your sunglasses but it's a massive failure if she dons another brand's eyewear when sunning in Los Cabos. "One of the classic no-no examples in the relatively recent past [is] somebody's paid seven figures to go rep Coke and then somebody takes a picture of them on their own time and they're downing a Pepsi," Karlitz says. "It really is about doing the homework. In the end of the day there just needs to be real relevance between that entertainer and the product or the cause."

What's your compelling pitch?

You've done your homework, see a good fit between your offering and a celebrity's interests and now it's time to reach out to his or her publicist, or someone else in the inner circle, such as an assistant. "Don't give them a two-page email," Karlitz says. "Two, three paragraphs tops. Who, what, where, when why. I call it the 20-second rule. If you have something compelling that you can put in those 20 seconds and if you can get it to the right person, I'm going to say there's a better than one out of two chance they're going to read it and if it's something that's semi-valuable they're going to pass it on to somebody." Even better: In the first line mention someone they know who recommended you reach out. Again, it's all about doing your homework.

How much are you willing to pay?

Depending on the level of celebrity you can expect to pay anywhere from tens of thousands of dollars to many millions. Consider the jewels and evening gowns stars are often paid to wear to the big Hollywood award events. "At the end of the day that kind of association is all about how much can I get and how badly do you want me?" Karlitz says. "There are celebrities that have long time relationships with their designers--Karl Lagerfeld and Armani--and they wouldn't dream of going to someone else. But anybody else, 'What are you going to pay me? If I don't look terrible in it, I'm going to wear it. And, in fact, if you pay me enough I'll still wear it if I look terrible. It's one night.'"