There are lots of information management programs out there that ask you to tag your notes, ideas and files (think of Evernote, Springpad, PersonalBrain, etc).
Regardless of the program you use, the purpose of adding tags to your data is to make it more descriptive and therefore easier to organize and find later.
Having used 4 or 5 different tools that use tagging, none of them provide any guidance on how to do it efficiently (read best practice). So here is the approach I have adopted.
My first tag is a General Category tag to help me quickly determine the overarching purpose of the information. If I clipped an article about optimizing a Windows 7 setting in Evernote, then my first tag may be “Windows 7”.
More Specific Category
My next tag is usually a more specific tag. In the example above, it may be “Optimization” or “Tech Tip”
There may be occasions when I may add a third tag to identify the source of the information. In the above example, let’s say the article came from Lifehacker.com, then my third tag may be “Lifehacker.com”. This is an optional layer that I sometimes use.
Define your format
Generally you want to define how you will be writing your tags. Which letters will you capitalize? Will you use the singular or plural form of a word? Define this ahead of time and stick to it.