If I had a buck for every time I’ve cautioned….  Well maybe not that many times, but it is important to your stillwater presentation to keep the tip of your rod down toward the surface. Less slack is imparted to the fly line (above, there is a fair amount of slack to take up in a strip set or by swing the rod to the side to set the hook) if the tip is down to, or even in the surface (Intermediate /Sinking lines). 

If you cannot pick out your fly in the distance, then focus on where the line enters the water and watch for the line’s bow or sag to tighten or jerk away. On smoother waters you can see ripples or pulses jolt out from the sides of the fly line indicating a take. All this is easier to maintain if you just ‘keep your tip down!’ Geeze that lake looks inviting about now.