I'm too much of a perfectionist for my own good and probably work to too high a standard on half of what I do. I don't use SignLab but I'm sure it has "power tools" for cleanup. Anyway here's my approach which very much adapts to the nature of the artwork:
The main tools I use are:
FlexiSign
Adobe Streamline
FontExpert and Typograf
Artwork, for purposes of this discussion, falls into the following classification:
1. Black and White original or either color or grayscale.
2. Strong reference points such as text, borders, underscores and geometric shapes or irregular in nature.
Method 1
A black and white image of a dog. (Little or no visual reference points)
1. Scan in Photoshop at 300 dpi, black and white color mode. Most autotracing applications provide the cleanest and most faithful traces of b/w at 300 dpi. They're fined tuned for that setting. No more - no less.
2. Inspect scan in Photoshop and cleanup any imperfections. Save as TIF
3. Open in Adobe Streamline, set tracing parameters appropriate for the artwork and autotrace the image. Streamline is incredibly fast. Inspect the resulting trace and either keep it or delete and repeat after changing parameter settings. When a satisfactory result is achieved, save as Illustrator AI.
4. Open in Flexisign and use the various power cleanup tools as necessary. Save again as AI.
Method 2
A black and white image with text and a graphic with clean geometric shapes. (Lots of visual reference points.)
1. Scan the image as grayscale in Photoshop for a size of 8 to 10 inches wide or tall at 200 dpi. Touchup very little or not at all. Rotate image to precise horizontal alignment. Save as TIF or JPG depending on my mood. Adjust the opacity of the image to a medium gray to more easily see your vector lines when it is overlaid with vectors later.
2. Identify all type styles used in the graphic using FontExpert and/or Typograf. Install all fonts needed into operating system.
3. Open saved bitmap image file in FlexiSign and size up to about 24 inches wide or tall. Lock the image. We now have a template ready to have a vector image created on top of it. We will follow to a large degree the same approach as was used to create the image originally.
A. Set all type, modify size to match the scan, modify any expansion, condensing, slant etc. that may have been applied to the type originally. Position each line of type to match the baseline of the corresponding scanned type. convert all type to curves. Using the left and right arrow keys, nudge each letter into place to match the position of the scanned characters. Do not move any character up or down even if the scanned is slightly off on an angle from horizontal.
B. At this point start thinking like a draftsman for duplication of the graphic. Look for geometric shapes that are part of the image or that have been cut out of the image. Look for all lines that are on the square or have a parallel relationship to other objects. Use the rectangle, circle, and oval tools to create the shapes, size them and position them on the scanned template. This will provide you with much higher quality results than trying to lay down a path with the pen tool. Let's say we want a circle with a series of 3 horizontal stripes of negative space breaking it up into segments. We could just select the pen tool and start hand tracing it but it would never be as near perfect as if we drew a circle and three rectangles, size and position them, and finally use the rectangles to cutout the circle. And it takes far less time.
C. Use the pen tool to draw Bezier paths for the balance of the graphic as needed. (In our example no hand drawing was needed). Use the weld and cutout tools to combine the shapes to complete the graphic. Use outlining, shadow and distortion tools where appropriate. When complete, save as AI.
D. In the example above, the main circle was cutout by three rectangles across it. The female symbol was created by outlining a circle to create the second circle. The two circles were combined (compounded) so the center is a hole). Next the cross was created from two rectangles. Finally the three objects were welded together. Next it was centered in the segmented circle and sized. Next the symbol was outlined and the outline used as the cutout object from the segmented circle.
Variations come into play when color is introduced but the methodology is the same.