2001:
There isn't a quick answer. Start by redefining the import feature.
1. Always try automatic first. Select Heal Geometry > Automatic > choose the geometry to fix.
2. Next try to zip gaps. Use the default gap distance for the first run. Select Heal Geometry > Manual > Zip Gaps > AutoSelect > Zip Gaps. If it doesn't pick up all gaps, use the Max Gap Dist option to specify a larger value.
3. The remaining gaps will be fun. Review a pair of surfaces that don't match up. Choose your victim according to which one looks malformed. Select Heal Geometry > Manual > Edit Boundary > Choose your surface > Select Contour > choose all or choose the endpoints of the bad edge. Practice with this feature will teach you when to use one or the other of these options.
I would probably delete the bad edge and then replace it with a connect or intersect. When you use the connect, it doesn't necessarily attach it to the existing curves. If Combine is an available option, pick it and connect the new curve to the existing curves before completing the feature.
If one corner of your surface doesn't match up to the corner of the other surfaces you can move that end point with Modify > Move Vertex. Play with all the options here. They all work well for varius circumstances. Once you get a clean edge between the two surfaces, finish the surface modification and try to zip gaps again.
4. Sometimes the surface just won't match up with existing surfaces. In this case, use Exclude Surface to remove the bad surface. Complete the redefine and build a patch surface with Pro/ENGINEER's surfacing capabilities. Then redefine the import feature and merge the Pro/E surface into the import feature with Collapse Geom.
Another option is to use Import Data Doctor (IDD). If it is a small fix, I would follow the steps above. If it is a truely ugly file, use IDD.
In most cases bad surfaces come from IGES files. Pro/ENGINEER can import so many file types now that it is relatively rare to have to resort to IGES. If you can, get a differnt file type, STEP, Neutral File,CATIA V 4.2, ACIS, etc. This list only grows with the release of Pro/E Wildfire.
Hope this helps.