Matt Gemmell at his best on how he uses tags in OS X Mavericks:

I’ve always struggled to use tagging systems. My tendency is to over-apply tags, resulting in hundreds of different ones in use, barely providing more retrieval value than just searching by the file’s contents. Since everything is constantly indexed on modern operating systems, I see tags as more of an organisational and categorisation system.

If you have struggled to use tags in an efficient way in Mavericks, this article is for you. 

I’ll try and stick with Matt’s suggestions. Limit the number of tags, maybe as few as the colours available and let Spotlight do its job.