Jim;
I guess the obvious place to start is to measure the lines per inch already on your gunstock. Go to Brownell's Inc. or Midway, USA and buy a beginner checkering set in the LPI needed. Of course buy the extra single line cutters as they will be most useful. Brownell's has a small booklet about checkering that is most helpful in getting started.
All of the comments above are valid and need consideration too. You will learn as you go and you will find that some methods don't work for you as well as they do for others. Be flexible and try other's methods and you'll find a "style" all your own that will make you proud of what you do. Just don't figure you will be perfect your first time. I have been checkering for over 20 years and still make mistakes. (Just looked up amateur in Websters..."someone who does something for pleasure, not for money...nonprofessional." Doesn't say anything about not being good at whatever it is.)
Above all else....GO SLOWLY, BE PATIENT, REST OFTEN.
