The small sized snails like Ramshorn, pond, bladder and Malaysian Livebearing are beneficial. They eat all organics, which is primarily fish excrement, thus breaking it down faster so the bacteria can get at it quicker. Snails get places the aquarist never could, so they are your helpmates. Now as for numbers.
These snails will reproduce according to their food supply. The more organics, the more snails. How much you feed the fish is obviously thee issue here, so the more you feed and/or the more fish you have being fed, the more organics. Don't overfeed, don't overstock, and be regular with maintenance especially partial water changes (50-60% once each week minimum) with a vacuum of the substrate in open areas, and keeping the filter media well rinsed will all contribute to reducing organics.
I have hundreds in my tanks (pond snails and MLB) and I know they are there because they have food and the faster they get rid of that the better the fish and biological system will function.
But if you really do want to reduce them, there are some do's and don't's. Never use chemicals, as these get inside the fish and are not beneficial at all. Never acquire specific fish that "may" eat snails unless you really want the fish and can provide what it needs (numbers for shoaling fish, tank size, etc.). Picking the snails out when you see them, or during the water change, is safest. Some use a lettuce leaf in the tank at night (snails will be out and about during total darkness) and in the very early morning the leaf can be taken out usually covered in many of the snails. The leaf should be lying on the substrate to collect the most snails.
Then comes the next problem, getting rid of the captured snails. You must kill them. Flushing them down the toilet, down a drain, or tossing them outside is not wise, as most of these can easily survive and if they get into the local ecosystem can decimate the natural snail species. This is a very serious issue; Assassin snails are discouraged if not illegal in some parts of the US because they can kill off the local snails rapidly.