Meta data is a powerful tool which grows in importance the more images you have. On this video Jay Goodrich (from CreartiveLive) explains how useful meta data can be when sorting through your photo library and gives some useful tips.
Adding keywords to your images is an amazing way to help you sort between thousands (some times much more) images and find just the ones that you want. Stars and color rating is also helpful however sometimes writing down dozen of keywords is exhausting.
Here comes a useful Lightroom plug-in called Keyword Master which you can try (and later buy for about $12) that helps you find good keywords quickly. It was developed by photographers who are interested in selling their images online however it can be useful for almost anybody who has a very large database of images.
If you want some more basic guide to adding metadate to you images check out the following video by Oliver Pohlmann: