I got carried away with following too many people on Twitter on one of my accounts (@2edinburgh) and hit the 2000 following limit without ensuring that I had engaged with enough people en route. Twitter keeps an eye on the following-to-follower ratio, so won’t allow you to follow more people unless a similar number follow you back. So I needed to pare back the number of folks I was following to allow my follower numbers to catch up.
I found the tool UnTweeps.com very helpful – it allows you to see who hasn’t Tweeted for a while and unfollow them by simply ticking a box. You can set the inactivity range to “Hasn’t Tweeted for 30 days” or 60 days etc.