Tagging, need some help!

I use tagging here on Electric Weekend in order to filter and sort my content and for some reason lately I have been reading/seeing a lot of stuff about it. I’ve kind of developed a new understanding for how tags should be used, and as a result I want to remove/streamline some of my tags. If anyone out there is experienced in this, or knows how I can remove some and tag older posts with similar tags to the newer posts I would be very interested to hear from you.

What I want to do, is shrink my tagcloud. It has too many tags in it that are very similar to other tags (some are singular, others plural etc) as well as having too many tags that only relate to one post. It’s these tags I want to tackle and then re-assign more relevant tags to the posts. So if anyone has advice about doing this, then please let me know!