With the strainer engaged, use the knob to loosen the snares until the drum sounds like a tom tom; then tighten them while tapping the drum very softly (like, 1 cm strokes) in the center of the head, with a stick. Keep tightening them until you get a sound you like. You'll notice that if you continue tightening the snares, the drum will eventually start sounding like a tom tom again, which you don't want. Normally the area between the too-loose and too-tight tom tom sounds is what you have to work with, according to your taste.