If your clock has a pendulum use the following method.

Check the clock against an accurate source like a cell phone or digital clock. After 24 hours make note of any discrepancy in the time. Stop the pendulum to move the pendulum bob up or down to change the pendulum's effective length. If the clock is running fast, move the bob down or turn the nut to the left. If the clock is running slow, move the bob up or turn the nut to the right. Restart the pendulum and reset the clock hands to the proper time.

It is easy to remember: lower is slower and left is lower.

How much adjustment is needed depends on how much time is being gained or lost. General rule of thumb: One complete turn (360 degrees) of the nut is equivalent to 1 to 2 minutes of time change per day (24 hours). Time regulation is tedious and can take up to 2 weeks to set properly. All mechanical clocks are affected by barometric pressure and temperature variations within their environment.

The best way to regulate the clock is to find the clocks time equation. 

1. Set the clock to the correct time and allow it to run for 24 hrs.

2. By example let's say the clock is 5 minutes slow in 24 hrs.

3. Make a note that the clock is 5 minutes slow and raise the pendulm to make the clock run faster by turning the nut on the pendulum to the right 360 degress or 1 full revolution.

4. Reset the clock to the correct time by moving the hand up 5 minutes.

5. Check the clock 24 hrs later to see how much time has been gained from your 360 degree turn of the pendulum nut. Let's say the clock is now only 3 minutes slow.

6. You now have a time equaltion for the clock. 1 360 degree turn of the nut made up 2 minutes of time in a 24 hr period.

7. 5 minutes the first day. 3 minutes the second day after 1 360 degree turn of the pendulum nut 5-3=2

8. The time equation for this clock in this example is 1 turn equals 2 minutes per day.