Mike, I remember well the first few times I dealt with the drywall mud process; it's a skill in many ways you really only learn from experience. You can be shown how, told how, and still you'll sand and skim 'til your blue in the face trying to get it right until finally one day you mystically find the secret from trial and error.
But, 2 things that will help you here; when it comes to taping knives, wider is better, and second, you don't really try to get your joints and repairs truly "flat," with the possible exception of the tapered edge joints. The trick is to make them so gradual that they disappear; this is done by using a wider taping knife, and feathering your mud "float" over a larger area.
If you don't have one, pick up a 12" mud knife; this will help you a great deal in getting a smoother surface without as much sanding. Use your 6 or 8" taping knife to do your initial taping and mud bed, but for your final use the 12" and taper your mud finish out over a wider area. This will soften what might be a visible "speedbump" of a joint line to a very gradual transition which will hide better when finished. It should cut down your sanding, too.
There's nothing wrong with skimming the entire surface, as you asked, but hopefully this added info will help you keep your labors to a minimum.