The single best rule I've found for getting to use my miles is to be creative and to keep calling until you get an agent who is willing to help check multiple alternatives. If you get an unhelpful agent who hates their job and just says "nothing available" (this is very common), thank them politely, hang up, and try again, until you succeed. In my case, I was booking summer vacations for my entire family, when I needed multiple international award tickets on the same flight and wanted to travel in business class.

For example, two years ago, Delta had no awards to Paris or Lisbon. So we got to Lisbon by flying on an award ticket to Brussels and then Paris to Lisbon, leaving the Brussels to Paris segment open -- I did my research and discovered there is a very fast train from Brussels straight to CDG airport. A bit inconvenient, but we did it and the train (the Thalys) was quite nice.

On United to Tokyo last summer, we went to Osaka and then had a domestic flight to Tokyo -- except on the day of departure, I convinced the ticket agents to switch us to the Tokyo non-stop at no charge!

Be creative, do your homework, keep trying until you get a helpful agent: that's what has worked for me.