The short-term traveller can usually get a Leave-of-Absence for a 'sabbatical', and return to the old job and living conditions, if the company has such a program and will approve it. This may be a necessity to prevent disrupting the family. Consider the option of Leave-Without-Pay if you do not have enough vacation time. Long-term travellers usually quit their job, sell or lend most possessions, place the rest in storage, and return when the funds run dry.
If you are not able to leave work for a long trip, you do not have enough money, or you do not want to race through a few cities, you can always decide later to separate a slow, expensive, long trip into segments. By planning to see the whole world, you will also realize which places you want to see first. If you miss places during your trip, you will already be prepared for future trips.
I do not suggest that you try to see it all in one trip, otherwise you are only going to see a bunch of airports and ugly cities. It is better to spend your time getting to know fewer places than running around collecting passport stamps. Spend time in one location, see the area, the people, the towns and villages, and then move onto the next stop.
To get a realistic estimate of the length of your first trip, list all the cities or countries vertically. Then give each the number of days you would like to spend there, taking travel time between cities into account. Consult travel books for reasonable estimates on ground travel time between locations. You can use a calculator, however a spreadsheet will add the days for you. A word processor is also handy, because it allows you to easily re-arrange your destinations as you prepare for the trip.
This worked pretty well for me on my first trip since I realized I needed to reduce the number of cities and countries I was planning on visiting in a given time. Now, I just look at the size of a country and my level of interest in it, then figure at least 1-2 months. There were many things to stop for, so most of the places I was racing to get to the border before the last visa extension expired. When you have a time limit on your visa, it is like having a string with knots that you can drape on the map any way you want, but it is gets shorter every day -- the trick is getting out before the visa expires, which isn't easy in a place the size of China. When you are travelling long-term, your plans change about every five minutes, as someone is always whispering an interesting idea in your ear. If you are on a short trip (for example: summer holiday from school, or taking a year off before graduate school), and have set dates for transiting between cities, then you will not find yourself in these circumstances.
Most people are doing a one-year route. Regardless of how much money you have, I now suggest returning home after a year for physical and mental reasons, if you are new to long-term travel. You can go pretty fast for about two or three months, then you burn out, Eventually, somewhere around the six-month point, you realize what the proper speed should be. Many people I have met and corresponded with started getting homesick after nine months. Going home on a yearly basis juxtaposes what you are seeing and reminds you of the good and bad aspects of travel, just in case you forget them, like I started to do. You change after a year and it is good to get home to see how. It is also important to stay in touch with family and friends.
If you want to see many places, consider two separate one-year trips -- the cost of tickets will be about the same since the side-trips get costly, and you can visit regions far apart that wouldn't easily or affordably be done on a single ticket. If I had gone on two 1-year trips, then I would have dropped off some stuff, picked up some stuff, and been better prepared for the second half. I no longer think of it as a Big Trip, more like the first of many Extended Trips.
"Another way to approach this is to have a more detailed idea for the start of your trip, with probably more accurate (but still wildly wrong) estimates for time; and then vaguer plans for the rest of the trip, with maybe not even all the countries, except those you really don't want to miss. I strongly recommend flexibility as the key to planning. You generally need to know some imminent plans -- but the long term can be more flexible. Just guess at about how long you want to be away -- most likely this will change as you either get very sick and are forced to return home; or have such a great time that you need a lot longer; or you run out of money." <Chris Finlayson>
"I do not think you can or should plan the duration of your trip by adding up a schedule of time at each destination, unless you have a limited and precisely dictated amount of time for the trip (say 2 or 3 months). Instead, decide how long you want the trip to be, then let the trip expand to fill the allotted time once you are on the road. The idea of seeing the world in a year strikes me as ridiculous, even a lifetime would not suffice. Take all the time you have, and realize everyone spends more time than they plan. Remember to pace yourself slowly enough to actually experience the places you are passing through. The best times I have had are when I just hung on someplace for a much longer period of time than I had planned, or than I needed to see the sights." <Larry Lustig>
"One time-consuming task that we did not anticipate was running errands. At least once a week we would spend half a day or even a full day running errands: refill first-aid kit, check on flights, phone home, shop for clothes (e.g. socks, underwear) and toiletries, buy postcards, buy patches (for our backpacks), buy notebook and/or pen, plan where we were going next and what we wanted to see, buy bus tickets, get maps, mail stuff home, buy traveler's cheques, buy food, etc. You do not do all these things each week, but there is *something* that needs doing each week. :-)" <Russell Gilbert>
"Man, I'm jealous!!! About 3 years ago my wife and I went on a six-month round-the-world trip -- WAYYYY too short, even a year might seem not enough." <Eberhard Brunner>
"I started off surfing in Indonesia and visiting friends on Java and Sumatra. After about five months I knew that I could not go home so soon. There were so many interesting places to visit, I was spending so little money, and having such a great time that I decided to extend my trip. I was gone about ten months before I seriously thought about turning my trip into an RTW." <Keith Conover>