Begin tightening the second nut on the side with the chain (usually the left side) with a 14mm

You should visually see the chain tightening and the sliders moving which marks the chain position

Tighten to where there is about ½ to ¾ inch of play in the chain.

Notice the mark of the slider on the side you tightened first

Tighten the opposite side till the slider is in the same position as the first side you tightened