If the air is very dry, much water evaporates from the cloth, cooling the thermometer. If the air is very humid, less evaporates which cools the thermometer less and a higher temperature is recorded. You can adjust the humidity by increasing the amount of water in the incubator or reducing ventilation. Turning is most critical the first week of incubation. The more often you do it, the better.
Commercial incubators do it every hour.
If you do not have an automatic turner, it is important you turn the eggs an odd number of times each day. This is important so you do not leave the eggs in the same position each night which is the longest period of time they go without turning each day. Just draw a line on the eggs. When you turn the eggs, the line should either be on the top or the bottom of the egg. Most eggs are incubated on their sides in small incubators.