For example, if you are in a business where you need to prepare lots of slide-based presentations, keep a separate document in which you store all of the useful graphics, symbols, contents page/agenda, title formats, diagrams etc etc, even animations which you could re-use in future presentations.
Every time you come across a useful symbol, graphic, technique or piece of formatting either in your own or in someone elses presentation, update your resource master with this for possible future re-use.
Then every time you need to prepare a new presentation you have easily to hand a kind of ‘library’ to draw from which can save a lot of time when creating new presentations. Not all, but particularly those where you would otherwise have wasted lots of time searching around for graphics etc that you were smart enough to save in your resources master.
The same is true for spreadsheets if you have formatting or formulas you often use, and also for keeping lists of useful online resources, websites etc (which you can also do using a bookmarking service such as Delicious.com but I still find it useful to store these in my own documents).