The correct pronunciation is a pharyngealized glottal stop. The best way to learn to pronounce this letter is to learn how to properly learn how to pronounce a Teth (ט) first. This is a pharyngealized voiceless alveolar stop. To make this sound, make your tongue into a cup. It should be pressing on your furthest back top molars. You should also feel an uncomfortable sensation in your throat, which might cause you to gag a little until you get used to it. Keeping your tongue in this shape, say 'Ta'. It'll come out sounding odd, and half way between a T and D. Once you can do that easily, you're ready to try an Ayin. The glottal stop is the sound you probably don't hear that occurs at the beginning of all the words that start with a vowel sound. It's easiest to hear the sound as the '-' in 'uh-oh'. Make your tongue into the bowl shape and say 'oh'. It will sound weird again in the same way as the Teth. That's an Ayin. Practice 'uh'-'Oh' until you sound like a Yemenite.