Mouth noise can be frustrating for a voice talent when you get behind the mic. Even the slightest sound that you don't necessarily hear in your every day speech, can be picked up by the microphone. The more you can be aware of it for yourselves, the easier it'll be in eliminating it during a voiceover recording. Please refer back to this list before you record.
To help eliminate mouth noise while you're recording, here are a few tips you can try:
1 - Keep yourself hydrated - drinking water when you already have a dry mouth won't necessarily remove the mouth noise, it might actually make it worse. The more hydrated you are before your recording, the less mouth noise you will probably have.
2 - Brushing your teeth and your tongue and using mouthwash right before you record. However, if your mouth is overly dry to begin with, sometimes using mouthwash can make it worse.
3 - Eating green apples, drinking cranberry or grape juice and/or using a hard candy to moisten your mouth (and then of course remove it when recording), a slosh of olive oil or eating a few greasy potato chips right before you record are also great tips!
5 - Be well rested! Your body is your instrument, the better you feel, the better you'll sound.