Anyone can invent a word. The difficult part is to get it permanently established in the language. To stand the best chance it should probably relate to a particular and fairly specialized subject. That cuts down the initial number of people who need to agree to use it. Failing that, it helps to be a well-known and widely read author.
Ordinary people can invent survivable words, though.
In 1924, in the middle of the Prohibition era in America, a competition was held to coin a word for a drinker of illegal liquor. The joint winners were Henry Irving Dale and Kate L Butler, who both came up with scofflaw . And that word survives in US English to this day, in the rather wider sense 'someone who flauts the law'. John Ayto is a lexicographer and word buff. He began his career in dictionaries at Longman, where he was the Senior Editor on the first edition of the Dictionary of Comtemporary English , and subsequently became Managing Editor of Longman Dictionaries.