I have at various times worked with three different approaches to developing history.
One of them is to begin at the beginning. Although this is attractive for story purposes, I find that modern history, and specifically the 20th century are insufficiently developed in the areas I need most. I am also relatively unfamiliar with Africa and its history, and with stone age developments and hunting and gathering societies, so progress is slow.
The second is to work forward through history, and pull back interesting peoples or other developments from previous periods. With each pass, I develop a century a little bit more. The chief difficult with this is that I spread myself a little too thin trying to follow everything, and it goes slowly. At present, I have reached the end of antiquity. This is where I can add information, as I am using this to incorporate notes from the older web-based version of the SKB, and occasionally look up developments in specific nations that I never got around it to including in it.
The third is to work on current events. I have recently been having success with a using a plan for specific periods, what needs developing, and why? For instance, in the20th (and the 21st century so far, I have been concentrating on Western Civilization, specifically the Anglic world of Britain, North America, and Australia, more specifically on North America, and even more specifically on the United States and major regions of the United States, down to a couple of major cities. For this work, I have mostly been developing the connections among peoples and cities, concentrating on those that are most relevant to whatever I am working with. I am finding, for instance, that many of the topics for which I have a well-developed history have poor connections to peoples, cities, and and social mechanics. For the 20th and 21st century, my development of Western civilization is much stronger that my development of Asian peoples. which is something I need to work on.
At one point or other I have worked on each of these to the exclusion of the others, and progress had been frustratingly slow. Giving a little time and attention to each may be more satisfying.
For fictional development, I am starting to use GURPS City Stats to get a picture of the major cities of the world, although this will be considerably improved by adding organizations using GURPS Boardroom and Curia. The new GURPS Realm Management is also helpful in developing particular nations, parts of them or combinations of them, although it is more geared toward active play than I am interested in right now.
I have let my cartographic mapping lie fallow for a time, but there is a growing need to pick it up again.
For my fictional wizard, I am so far doing better at describing where he is traveling in any given century, but not why he is there or what he is doing. That will come later.