A FishboneDiagram (also known as a cause-and-effect diagram or an Ishikawa diagram, after its inventor) is a tool for generating and organizing thoughts about a desired effect.
To create a FishboneDiagram:
Draw a circle and label it with the desired effect.
Draw a horizontal line out from the left edge of the circle (if you read left-to-right). This is the "spine" of the fish.
Brainstorm about the key categories of things that could cause the desired effect. For example, think of the processes, procedures, factors, steps, etc. that are involved in the situation. (This is often the hardest part, in my experience). Generally you should have 4-7 of these; if you have much more or much less, refactor until you get a manageable number. Draw these as "bones", or diagonal lines starting from the "spine" and moving outward; alternate above and below the "spine".
For each category, draw a horizontal line from the "bone" to the right (if you read left-to-right) for each cause in the category, and list the cause on this line.
For each cause, if you can identify something more fundamental (a "cause of the cause"), draw it on an additional diagonal line toward the head.
[EditHint: anyone want to try rendering this as AsciiArt? My attempts haven't been pretty...]
(Something like this?
Category A Category B
Cause A.1--\ Cause B.1--\
Cause A.2--\ _______\_____________\_____Desired
/ / Effect
/ Cause D.1--/
Cause C.1--/ Cause D.2--/
/ Cause D.3--/
Category C Category D
Though it would be more informative to see a real world example.)
Now that you have a pile of causes listed, look over them as a group. See if there are any root causes that show up on different bones. These are the first things you have to do to achieve the desired effect.
AdvantagesFishboneDiagrams are occasionally useful for initial brainstorming.
DisadvantagesFishboneDiagrams tend to be either far too simplistic or far too detailed in real world use.
These alternatives are more structured, to show how potential causes are related.
A constrained kind of MindMap, in which the central box is the desired effect, the outlying boxes are constrained to causes, and lines between the outlying boxes are constrained to indicate causality between driving factors.
SystemsDynamics? graphs, which quantify how driving factors affect each other.
Problem solving FlowCharts show what questions a good TroubleShooter? asks to solve the problem. You can develop the FlowChart incrementally.