What is an efficient way of planning solo-trips with so many unknowns?

This strategy works better when you have plenty of time: don't plan - just make it up as you go along.

Many years ago, I took a gap year after university. I decided to see how far from home (UK) I could get without using a plane. I bought a train ticket from London to Istanbul. This was a cheap ticket with no reserved seats but I could get off and on as I wished. I chose to get out in Paris, Venice, and Belgrade before arriving in Istanbul. I then found a cheap backpackers hotel and explored locally for a bit. I had no plans of what to do next. While there, I researched a little and found a boat to Samsum far east in Turkey. Again, I did not yet have a plan of the next step. My only advance planning was to get a visa for Iran since it was fairly obvious that I would need it. Eventually, I got to Malaysia without a plane.

It can work on a shorter trip. More recently but still quite long ago, I took some visiting friends from the UK to France for a few days. I bought a ticket for my car through the tunnel to France. While in the tunnel, I said: "where shall we go? We can turn right when we get out and head to Mont St Michel in France (an example of a nice place that I knew that we could get to in a reasonable time) or we can turn left and go to Brussels and maybe Amsterdam afterwards.

I could give more examples but it is a strategy that I like - just set off and make it up as you go along.

Additional: if you have access to the BBC then look for this programme: Race across the World. It is rather similar to my trip long ago (except that no film crew followed me). It gives a fairly good idea of how to make it up as you go along. It has caused me to daydream of another trip.

As Kate has pointed out in her answer - 'Anticipating something gives almost as much happiness as the real thing'.

But I do understand your anxiety and apprehensions. I have been on many trips with friends/family and also alone. I have been on trips organized by tour-operators/guides but most of the time they are completely self-organized.

At this point I can say I am fairly confident of my ability to plan a vacation from scratch and also deal with any unexpected happenings along the way.

But even now, I take a lot of time to plan and research the places I am going to. I find that the shorter time I spend on the vacation, the more planning I need to do to avoid wasting the precious little time I have. I work full-time, so I mostly take not more than 3 days off for a trip and I don't want to spend 4 hours waiting for a bus or train due to inefficient planning.

There are many ways to plan a trip depending on your preferences and planning style. One I choose is as follows:

1. Choose a place - it could be a city or a region.

   Eg: Prague, Western Italy, Southern India, Liechtenstein+Innsbruck, Poland etc..

2. Get a broad idea of what that place has to offer and what catches your fancy.

   Eg: I wanted to visit Poland. I knew I definitely wanted to visit Warsaw and also one other city in Poland - The most suggested ones in the internet were Gdansk, Wroclaw or Krakow

3. Narrow down the options based on your travel options and interests.

   Eg: There was good train connectivity from Warsaw to all the 3 cities mentioned before. So I had to decide if I wanted to visit the sea in Gdansk, watch the wonderful old architecture in Wroclaw or Krakow. I had 4 days, I thought, instead of spending all my time in the cities, I must go out into nature for a day and try out my new hiking shoes. On further investigation, I found that Krakow was close to Zakopane which was a base for some cool hikes in the Tatras mountains and I could also stand on the Polish-Slovenian border on top of the mountain. So Krakow is the choice I made- my plan was coming into a vague shape after all.

4. After deciding on the destinations and activities, you can decide on the amount of time you would spend at each place and this would in-turn give you an idea of what travel and accommodation choices to book.

   Eg: I booked a flight to Warsaw, a train from Warsaw to Krakow and a return flight from Krakow. One night in Warsaw, one in Kraow and one in Zakopane. There was a bus from Krakow to Zakopane, so I did not book it so that that part of the journey would be flexible.

5. Once the major portion of the trip as been planned and booked (Travel, accommodation and activities (tickets for tours, amus*m*nt parks, ski-resorts etc)), rest of the minor details can be planned at your leisure.

Of course, I did not do all this at a stretch in a single day, it took some time. But that was a fun thing too - I was spending my free time exploring about Polish history and rural Poland rather than watching cat videos on facebook.

One thing you must remember as a well-traveled and travel-loving soul is that, no matter which place or activities you choose, in the end you are always going to be glad you took the trip rather than not taking it :) Keep travelling and let not planning take the fun out of it!

To each his own, meaning there is no 'average'.

But, you are unnecessarily stressed about the prospect of having to plan a trip. You, broadly, have three options:

1. Don't plan. Just go, now, and figure things out as they happen.
2. Plan the basics (like, your flight and hotel).
3. Plan everything.

The more you plan, the more cost-effective, efficient and stress-free your trip will be. The less you plan, the more adventurous your trip might be.

You have to find a balance that works for you.

For me, I tend to plan/book expensive and/or infrequent travels (flight/train/bus) as well as accommodation. This tends to mean huge savings over booking late or on-the-spot. And, then, to read up on what I can do at my destinations, and decide later.

This is awfully broad, but I will suggest you try a different way of thinking. Instead of "I want to ski the week of Jan 15th" followed by "oh god I have not planned my ski trip" and increasing panic panic panic until you get to "too late", try the exact opposite.

List some things you like to do. Investigate some of them in more detail. Don't ask people to recommend places or locations: just as here, it's too opinion-based. Instead, think about what you value: cheap transport from the airport, great views, food, the quality of ski-ing, how crowded it is at a particular time of year, and so on. Research these specific things. Ask friends these specific things. Heck, ask here. Not "what is the best X in Y?" but "is X crowded in January?" "What does it cost to get to X from the airport?" and so on.

Plans will start to evolve. You will start to feel that one particular place is calling you. For the ski-ing, the food, the scenic train ride, whatever. Now you can start to put a date to your plan to that place. Not before this point. Now you can look at prices and figure out how to book and how to make it happen. You know how many days that place requires. You know your options for getting there. You know the costs of hotels and admission to things. Half the work is done, perhaps more. There's no need to panic.

If you get to that point and it's just a few weeks till your allotted vacation time, then this vacation won't be that trip. This vacation will be something simpler and easier, perhaps something you've done before. Next vacation will be that trip that calls you. There is always a next vacation, after all.

I frequently spend a year planning a trip. One 26-leg 11-island trip took two years to plan. I loved every minute of it. Dreaming of the volcano, the beaches, the hikes, the museums. Building a list of the things we would see and do. The reality was even better, but the dreaming was a great part of it. If you stop seeing that dreaming and planning stage as painful, but instead see it as part of the joy of the trip, you will do a better job of planning and enjoy both the planning and the trip far more.