(image from Canva) Have you heard of the methods: Ethos/Logos/Pathos, often used in presentations? Ethos refers to showing the credibility of your ideas. Clearly citing your information sources would be an example of it. Pathos is the method of appealing to people's emotions-- using sensational pictures, strong anecdotes, etc. Finally, logos is proving your argument with simple logic, and it can be done by using things like statistics. A good presentation utilizes all three of these according to the situation, so try analyzing your own and see which section falls under which method.
(image from Canva) To make the audience believe the things you are saying, sources are crucial. For example, if you were doing a presentation about global warming, you might use papers by scientists, and if you were reviewing a book, you might cite from critics. Your sources should be different according to the situation. Rather than using the first site that comes up after an internet search, you might want to use academic search engines designed by certain companies. These services will automatically remove any sources that seem unprofessional or lack credibility, so they will come in handy.
(image from Canva) Plagiarism just might be the most important factor to look out for in a presentation. When using someone else's ideas, make sure they are clearly distinguishable from your own. There are many forms of plagiarism-- presenting others' ideas as your own, using a work without permission, and announcing an existing product all fall under this category1. Learn how to cite and use copyright-free material to avoid becoming a criminal. If you do not want to go through the trouble, there are software that extract necessary information from websites and creates reference lists for you, so try looking them up.
(image from Canva) Peer Review is showing a colleague your presentation and getting advice from them. It seems basic, but it is an important step in improving your presentation. Not only can they notice your mistakes from an objective standpoint, looking at others present may spark new ideas in your head. Also, having an audience puts you under a kind of "pressure" you can't experience alone, so you will be able to practice in a more practical environment. For instance, if you are doing presentations at a school, split into groups and try peer-reviewing.