Marion, I'm going to respectfully disagree slightly with our friends above. I would record your guitar first with the pickup. Next overdub your fiddle, and last over dub the guitar through the microphone. Why? In the first track you can hum or whistle yourself through your tune since their will be no microphone on. It's hard to play rhythmn guitar with no singing or lead. 2nd your scratch guitar track will hold your fiddle to the rhythmn. Last you overdub the 'keeper' guitar track with the mike, and you will have learned somethings about how you want it to sound. I also suggest you keep your guitar as spare as possible, less is more; you want your fiddle to be always out front. Keep your alternating bass notes consistent. Good luck and let me know what you end up doing.