I include how to do this in my game: New World Rising: Adventure in the Land of the Ginn. Short adventures might have a long-term goal that is completed long after the present adventure becomes old. The minor goal is in this adventure, but there is something that was not completed or is left to do for your characters. This is called a hook in writing, you do this on purpose to hook your players into playing the next one. Now, all that other stuff about which system and how many characters and how long it is supposed to be is easier because you created your hook, all that needs to be done is chose something similar. I did this ONE other thing that this reply is too short to put it all on here. I divided up the adventure creation into seven sections then created 100 words that are descriptive for each section. Each section is an attribute of a human; thought. mood, emotion, etc. Anyway seven of them then roll per page randomly and you have your theme. The number of characters can be as many as you can handle (I have an optimum of 8 but can ref 16). Using the tables I created can be applied to any game. There is a one in one hundred billionth chance of creating the same adventure twice with my method. I got the idea from how an old Thesaurus book is set up, not like they are today in dictionary form.