Are there any ways to minimize or prevent your emails being marked as spam by the recipient?

Sometimes I realize people that I sent an email to never got my email, because my email was marked as spam by their email server or client or whatever. How can I prevent this from happening, especially when I’m not even really sending spam or mass emails, but an important email that someone on the receiving end needs to read? It is quite frustrating when that happens. Any advice is much appreciated!