I am indeed a Cat Whisperer.
Pretend disinterest in the cat, yet find random excuses to be near it. Cats are naturally curious and will want to smell you. Hold out your hand and let them choose to rub against your hand. Anything that makes that cat feel like it was all his idea, and he is in control, will help.
Keep your eyes hooded and blink slowly. This tells the cat that you are relaxed, and don't perceive it as a threat. They are likely to respond in kind.
Take a shuddering breath in through your nose, and let it out heavily. This tells the cat you are letting go of any tension or possible aggression.
Don't stare at the cat's face or eyes. Use your peripheral vision to look at the cat. Cats find direct stares rude, unless you are very well acquainted, or have a good reason.
Don't be forward. If the cat allows touching, on the face/head and along the spine are appropriate for a casual friend. Belly, feet, tail, and other areas are for close friends. Most cats will forcibly remind you that you're not being "gentlemanly". By drawing blood.
As IdahoRose mentioned, playing with a cat before you try to pet it is a good way to go, but trying to pet a cat immediately after playing with it is a bad idea. They may scratch and bite if they think you are still in play mode.
Cats will pay attention to a higher pitched noise with a questioning inflection at the end. I often use, "Brrrt?" I get better responses with a rolled "r" than without.
I have found that a hissing noise of any kind puts off a cat. This is very useful if you actually want to train a cat.
All in all, those are my suggestions for making friends with a new or strange cat. There have been very few times I have been unable to keep a cat from doing something I did not want it to do, or to get it do do something I want it to do. As long as you are entirely committed and extremely consistent, cats will respond. Most people are just unwilling to be those two things. 