Since I'm a highway boy and not a backroads boy...
After this years trip I learnt one very valuable lesson. Watch your route. Make sure your route isn't trying to take you down any limited access highways. I screamed every darn time I came to turn and saw 'Bikes Prohibited'. Totally irritating.
Generally, I know where I'm trying to go and first go to ridewithgps and point on the start location and finish location and let it draw out the route. From there I reroute to avoid big cities, unless I want to go into the city. I also try to reroute around any major climbs that could easily be avoided by a short 'retour'. Once I have the route selected then I start looking at the daily distance I'm planning on riding and look for a town roughly that far away each day and then I start looking for stealth campsites...typically baseball dugouts that aren't within eye sight of too many house. I use Google Earth for this idea. From there everything generally falls pretty much into place. I just have to wait for the date of departure and hope(so far hasn't happened either of the past two years) nothing forces me to delay the departure and throw the entire planning into the dumps. UGH

Otherwise, like the past two years I end up planning on the ride and throw away all me pre trip planning. Can't wait for the day when I actually go on a trip and it goes according to schedule...even remotely close for that matter.