If I understand you question. it would depend upon the profile you are trying to trace. Lines and Arcs are the best for control in SW2004(SW2006/2007 you have more control/dimensioning over splines which make life a lot easier). Again depending on your sketch I start with circles and lines to get the over all shape then I start trimming and dimensioning form there.
When you import you image make sure to move it some you will have a good datum point for reference. I try to put a hole, corner on the origin or if there is a straight edge I make that parallel with a plane.
I hope this help you out.
CJ Goodrich
Product Design Engineer
Leatherman Tool Group
Portland, Oregon