A flexible thermistor reading library. Calculates the temperature based on the Steinhart–Hart equation, smoothed by taking a number of samples.
SmoothThermistor can be found and installed through the Arduino Library Manager.
The easy and most common circuit looks as follows:
However, to get more accurate readings, you can use the 3.3V pin on the Arduino, which has less noise. Make sure your thermistor is fed using 3.3V, along with the AREF pin. The circuits looks as follows: