jQuery: $ is not a function

Okay so the other day I was adding some much loved jQuery script to a WordPress site but the life of me I couldn’t get even the most basic function to work. I reduced my code down to producing an alert when the DOM was ready, but still it threw the following error: Error: $ [...]
jQuery methods: .queue()

So today I came across a bit of a UX problem while using jQuery; I wanted to submit some form content using ajax but the feedback messages were flashing up so quickly they were illegible. The simplified situation I ran into was: The user would submit a form of data using ajax, Content would be [...]