As far as lessons learned, here's one thing I wish I had done differently. I'll suggest United's FF program as being "better" than American's, where I have the bulk of my miles.

My latest example is a trip to Europe I'm planning for the off season. I really wanted to use my AA miles, but all flights to my destination from ORD required change of planes (and often airports) in London. The fees that must be paid on free tickets are much higher, in my case double, if you have to go thru the UK. AA has it over United (Star Alliance) for off-peak travel to Europe as the mileage requirements are 40K vs 50K for coach, but the airlines choices are more extensive on United's Star Alliance and (I've read) better in terms of in flight service and amenitites.

Just MHO as someone who has to save for years to get a couple of free tickets.