One common mistake that many novice and some “expert” speakers make is to ignore the time limit. Most offenders only go over by minute or two where others wait until they’re practically booed off the stage to finish up.
In general, this is very poor practice and if you’re being paid to speak or even speaking for free for a non-profit, it unlikely that you’ll be invited to speak for them again. If you’re giving a presentation at work, your co-workers may feel become annoyed at you. Think about when you’ve been in the audience and the presenter went way over time. It’s never viewed positively.