Fold your lips over your teeth it's weird but it helps and it feels better for him too, lick your lips to make them moist also.Another thing that helps is if you fold your top lip in and make like a hot dog with your tongue to create like a pathway to guide him.There's also this girl on YouTube and podcasts that give tips and shares stories of experiences of almost everything her name is "sex nerd Sandra" I've taken a few tips from her and has helped in my opinion.

If you have a Nook or the Nook App you might try reading "The Little Book of Blowjobs" it helped me tons!