1 - Drink plenty of water before going under. Your mouth cant generate saliva when you are not properly hydrated
2 -Minty candy/sweets work too - used to pop hacks before every dive, after drinking water.
3 - This may sound strange, but regulate/control your breathing. If you are breathing (ie; exhaling) like trying to start a bonfire for 45 minutes, chances are you will feel like you have rolls of barbed wire stuck in the throat at the end of the dive. Regulating your breathing, via calm and slow exhalation does help minimise it. Of course, you will also need to be properly hydrated beforehand lah.
4 - If your pockets are fireproof and resistant to huge holes being burnt, you can change your brand of regulators to them higher-end ones. They seem to have magical powers that prevent the throat from drying up. heh. Having said that u still need to drink enough water prior.
oh, have I mentioned "drink plenty of water" already?