I know first hand that the sand trick definitely works. Another thing which works is dryer sheets laid on top of the soil and/or around the bottom of the pot where the air holes are.

Never heard of the beer thing. Neem oil doesn't do much as a spray for gnats, but neem put into water and poured into the soil when you water/feed helps. I wouldn't say it's 100% though. A quick temporary fix to cut down on their numbers is to hang a no pest strip in the area, for a couple of hours then ziploc it up and put it away. (make sure you're not breathing the air around it for long, and that other people and animals aren't exposed to it if you're indoors).

I had a horrid time getting rid of mine until I used the sand and dryer sheets.