As someone who has been a noob for a long time, I found there are some plugins for cleaning up the model that are helpful at the beginning:
Default layer geometry (get all your edges and faces back on the default layer)
Remove Lonely Vertices (join edges that have unnecessary vertices into one)
FrontFace tool (get your faces oriented correctly)
Make Faces (get faces to form, especially on imported edges)
Everyone would say work with the basics for awhile , and don't make the mistakes in the first place; but plugins like the above help you get back on track, 'cause things happen. Your approach to the work, as in other realms, is probably more important than what tools you have. Starting out one could quickly make a mess with some of the plugins out there.
There are some in the "must have" plugin index that will get you a step further like Joint Push Pull and Fredoscale. Don't forget Sandbox Tools which comes with your SU and can do a lot with contours and manipulating terrain shapes.