Open up a map of Europe. Take a look at all the countries and cities. Get a feel for their locations and the distances between them.
Make a list of all the places you want to go. Mark these spots on the map. Now mark the places that you absolutely must go with another color or larger dot.
Take a look at your marked-up map. Consider how long you have to travel and how long you wish to spend in each place. Also factor in travel time and your mode of transportation. If you are flying from place to place, then distance is not much of an issue. Still, flying between cities eats up half a day. Overland travel is significantly slower but often more enjoyable. For instance, traveling from Paris to Frankfurt by train, bus or car takes about 8 hours. Estimate how many days will be spend en route from one location to another.
Start eliminating places that eat up too much time. If a dot on your map is far away from the others, it will take extra time to get there and back. This is time that could be spent elsewhere. Unless it is on your list of "must-sees," eliminate it from your route.
Connect the dots. Start in the city that you are flying to and end in the city you are departing from. Most likely it will be the same city. In order to avoid wasting time backtracking, try to make your route a circle that begins and ends in the same place. Connect the dots in a logical order. Keep in mind that if you are going someplace small, you will need to travel through a major traffic hub first.
Consider time-sensitive appointments. If you want to be in Paris on Bastille Day or run with the bulls in Pamplona in July, you must schedule this and build the rest of your trip around it. If you are traveling in Europe in the spring or fall, also consider the weather. Try to stay in the south when it is colder, and move north as temperatures rise.
Use a calendar to plan your itinerary. Start by writing your arrival city on day 1. Don't underestimate the effect of jet lag and the amount of time it takes to travel from place to place. If you are on a plane or train for 8 hours, you will not feel like doing much when you get to your destination. Make some days strictly travel days. Also, try to stay in each place for a few days so you don't spend your entire trip just moving around.
