For me, travel is an adventure, but adventures do not happen by accident, so before planning an actual itinerary, I need to answer three questions: where do I want to go, why do I want to go there, and when do I want to go? Those three questions are taped on my computer monitor as a reminder so I can't forget them - they are that important. I have used and refined my system over fifty years and planning is pretty much routine for me, but for inexperienced "solo travelers," this is how I go about it.
My travel "mantra" is, "There is always the next trip." With that as a reminder, I usually do not plan trips that cover too much territory or include too many places. I have had a very recent example of a trip which I should have heeded my own advice (see "Making the Same Mistake - Again... .").
So, going back to the questions, the first question, Where do I want to go? is the easiest of the three. Just about everyone wants to go somewhere, however, travel in Europe is expensive and time consuming, and unless I have time to burn (never), it is important to pick places that are within reasonable distances from each other. My idea of an adventure is not to see the countryside by train, so if I am taking a two week trip, I must keep the distances short or I will be spending too much time on the train. For example, if I am flying into Paris and then want to visit Prague or Budapest, I will lose about a day and a half to travel time (each way), and that is about twenty-five percent of the trip length. Even if I were to fly, I would still lose at least a day, and besides the time lost, moving (especially by air) is a hassle. So, with that in mind, I keep my travel times as short as I can. I pick base cities and take day trips which include a maximum of two hours of travel time each way. For example, using Munich as a base city, I can visit Munich, Regensburg, Nürnberg, Stuttgart, Würzburg, the Black Forest, the Disney castle of Neuschwanstein, and many, many lovely German towns. Munich is also a great base city for Innsbruck, Salzburg, and other beautiful Austrian Alpine towns. In short, Munich would be a great base for an entire two week trip. The same is true for cities in every country all across Europe. I try not to move more often than once each week because each move costs half a day plus travel time.
The next question is Why do I want to go there? I never go to Europe without having a basic reason for visiting a certain place. For example, my descendants are from Scotland and I love visiting that country, but I always visit Ayr and the Isle of Skye because that is where my ancestors were from and the area is interesting to me. That is just my reason and there are many others including ancestral homelands. Sometimes I have heard from other hostelers that a certain location is really worth a visit, and sometimes I just want to revisit a location that I truly enjoyed. The point is to have a reason, almost any reason, to visit a place. Then, if there is a city nearby that can be a base for day trips, look at a map to see what else is within the range I mentioned above. Caution! Because a place may look close to another place, don't forget that there might be mountains between the two and what looks close may be quite distant in regards to time. Having a reason to go to a specific place adds purpose to your journey, and that will add to your enjoyment of your entire adventure.
The last question, When do I want to go? is more about a person's own schedule variables. For example, a teacher is limited to specific times of the year when school is not in session. Others cannot schedule vacation times at certain parts or months of the year. For years I had limitations that caused me to travel in the spring of the year, and that is still my favorite time.
Travel seasons are called "Low," "High," and "Shoulder." For much of Europe the "High" season is from June through August. The "Shoulder" season(s) are from March 31st to May 31st and September through October 31st. The "Low" season is from October 31st to March 31st (except for mid-December to January 1st).
I prefer to travel in the spring of the year for a number of reasons. First, if I fly before March 31st the airfare is much lower. Second, the spring is when the shops and businesses are looking forward to the arrival of tourists as opposed to the fall season when the tourist businesses can't wait for the tourists to go home. Third, the weather in April is usually pretty mild and can be just glorious.