The new Twitter guidelines, published today by the Crown Prosecution Service, come in the wake of a series of high-profile social media abuse cases during 2012.
Footballer Daniel Thomas, who plays for Port Talbot Town FC, was suspended for a game and fined £500 after posting an abusive Twitter message about Olympic diving star Tom Daley.
Mr Thomas, who later apologised, was at one point arrested over the homophobic message.
The director of public prosecutions, Keir Starmer QC, though, said the tweet was not a criminal offence, despite being offensive, and was not intended to be read by Daley.
More top news
David Cameron sets out his case for British jets and drones to strike so-called Islamic State targets in Syria in an address to the Commons.
A drink-driver who "destroyed the lives" of two mothers was allowed to have his curfew lifted so he could go on a foreign stag party.
Demonstrators have blockaded the entrance tunnel to Heathrow Airport in apparent protest at plans to build a third runway.