What should be a relatively simple planning task is easily made complicated by trying to do and see too much and/or visiting too many places. I do not try to make a journey a "Trip of a Lifetime," but rather think of it as my "2012 Trip to Europe." (If money is no object, you don't need to be reading this.) Why spend $5,000 on one two week trip (which is easily possible) when for the same money, three trips of the same length can be taken? That's right - three trips!
When thinking about an eight week trip (I know that I go back and forth between two and eight week trips, but this part should clear-up any confusion), I look at a possible total of eight base cities, or one move per week. A two week trip would mean two base cities and a three week trip would mean three. Each base city requires a full day for travel, which allows for six days of sightseeing each week.
A Two Week Trip In Germany
Parenthetically, my first priority is to try to get an open jaw air fare which would allow me to fly into Munich and out of Frankfurt. Failing that (for whatever reason) I would have to schedule a full day for the trip back to Munich.
Using Germany as an example, if I fly into Munich and check into my hostel, I should have at least a few hours to get acclimated to my surroundings and the locations of of the closest grocery stores, Metro stations, tram and bus stops, and the all-important Tourist Information Office (my first stop - always). The TI office will give me any information I need about day trips as well as the sights of Munich. I would then plan on three days in Munich, a day trip to Salzburg, Austria, a day in Nürnberg, and a day in Nordlingen (a walled city with a lovely altstadt (old city). After making my plans for the week, it's a short walk to the grocery store for cold cuts, bread and rolls, soda, water, or beer, and anything else I need. Then, it's back to my hostel to prepare supper and look through the brochures I picked up at the TI, and to plan my next day. On my seventh day I would move.
The second week I would try to go at a little more relaxed pace and I would go down the Rhine River stopping at the numerous lovely towns and castles on both sides of the river between Koblenz and Mainz. I would stay in Koblenz at the hostel in the Festung (Fortress) Ehrenbreitstein (one of the largest fortresses in the world) and take short day trips to Rüdesheim am Rhein, Bacharach, St. Goar, Oberwesel, Braubach and Castle Marksburg, and a relaxing final day in the Fortress itself with its' museums and and most impressive battlements and grounds. Finally, it is a short train ride to Frankfurt and my Open Jaw flight home.
The Other Six Weeks
Using the first two weeks as an example, it is a simple matter of picking other base cities (one for each week) and exploring the area around it. For example, if I were to stay in Germany for another week, a good idea would be to stay in Berlin, using three days to tour that great and lively city, and taking day trips to Potsdam, Dresden, and Leipzig (all of which were in the East Zone until 1989).
From then on, it is merely a matter of finding one base city for each week I will be traveling. In Belgium I would use Ghent as a base city to visit Brussels, Brugge, Antwerp, and Liege. In Austria I would use Vienna as a base city (I visited Salzburg and Innsbruck from Munich, remember). Vienna takes at least three days and the next three would be spent on Danube cruises to Melk, Krems, and Durnstein. Italy has base cities throughout the entire country on the Mediterranean side and the Adriatic side.
Italy and Greece are kind of special for two reasons. First, they were the centers of civilization for centuries and each has so much history and art that they can be dizzying. Second, for the above reason, they are both best enjoyed in small doses. I don't believe that either country can be truly known and appreciated without living there, which I have not. Be prepared for extra adventures in both countries if you plan on driving, or count on trains and buses being on time. My best advice is to relax, go with the flow, and enjoy the adventure just like the Italians and Greeks do. Life is a wonderful mystery.