There are many useful conversations on Mathematics on Twitter. Now just in case you hate Twitter or have no interest in it – you can still follow useful conversations and follow links to resources without even signing up to Twitter. I find Twitter a little like a lucky dip – usually in just a few minutes I find useful resources or the latest educational news.
For Mathematics teachers I would recommend the following:
NCETM Twitter chats #mathscpdchat every Tuesday from 7pm to 8pm
All the links above to Twitter list the tweets in time order (Live); note that you can choose Top or Live;
@Desmos for the latest on the fabulous graphing calculator
It is possible to create lists on Twitter, for example follow news releases as they happen from Ofqual, DfE and the exam boards on Twitter, using this Examinations list. (You can follow this list without subscribing to Twitter.)
If you are interested in learning more about Twitter see the very clear Twitter Lingo guide from Mashable.