Keywording can quickly get out of control. And, you can vary between draconian and loosey-goosey, easily.
Enter this useful guide from MediaValet. An article of perfect length, it offers 14 best practices worthy of printing out and putting on your wall, if you are a digital librarian! IMHO, the last one may be the most important: Watch your spelling!
At the end, there’s also a link to a step-by-step guide (registration required) to implementing your DAM, and how it is like a bake sale.