The most important before strating is to have some knowledge about the patch layout creation... It is impossible for me to teach you how to do... Also the most important is to have a (your) logical way.

If it is your first time to rebuild one existing shape, you can try to reproduce the styling line of this Door.

For me it is the most important STEP. If you can do that "correctly" this 2D curves (I will tell what is correct for me later) 40% of your work is done!

In this video you can see some tools who can help you for clean the scan data (called Mesh in Alias)... As someone know, other software can help you to divide your mesh according to the curvature transition shape and detach "automatically" your mesh as you can see in my video. In Alias if you want to do that you need (in 2012) do by "hand" as I showed you in this video...

At the end we have the most important styling line of this Door trim in 2D.
Take care to manae the parameter of these curves, the minimum order needed for make the styling shape.
IMPORTANT: Use maximum degre 5 curve (6 control points) at this time.

For Class A (in general) try to use for your "main surfaces" called also "primary surfaces" 5 degre parameter. You can use degre 6 and 7 maximum for many standard for the transitional surfaces called also secondary surfaces if you are using G3 continuity...

One thing to keep in mind: it could be possible to increase the number of CV if you need to add more "quality" of your shape. BUT it will be pratically IMPOSSIBLE to reduce the number of CV if you have got too many at the beginning!