There are basically two ways to pronounce the letter R in French. The first, and hardest for most people, is the back-of-your-throat 'coughing' one. It's really not that difficult if someone explains it right. All you gotta do is pronounce an 'H' like you're trying to hack something onto the wall. Then, all you must do is incorporate this sound into the middle of several common words. For example:

Merci (thanks)
Porte (door)
Trente (thirty}

The second way is slightly softer and gentler. This is usually used when the R is at the end of a word. Examples:

Pour (for)
Bonjour (hello)

You are now on your way to impressing everyone!