A blast of hot air for a few seconds will defog the dampest eyepieces, mirrors or lenses. Commercially available 'dew zappers' are basically modified electric hair dryers. You will get better with practice. Your brain learns to see more as you do more observing. Sometimes if you are very tired you won't see as much.
Some drugs can make seeing dim objects more difficult.
Try to observe in a comfortable position. If you will be looking at very dim objects try to keep your eyes protected from bright light the day before you observe. Try looking a little off to the side of the object. Try tapping the scope so that the image will move a little in the field. Try different magnifications.