How do you keep important emails on top?

If You're Constantly Forgetting About Important Emails. You'll love the “pin” feature. Just hover over an email, tap the push-pin icon, and voilà—the message is put front and center in your inbox until un-pin it. You receive extremely detailed instructions for a project. Instead of having to do a search for the message each and every time you work on the task, just pin the email to your inbox. You’ll have it open in your browser within two seconds. 

The only limitation of pinning emails in Gmail by starring them is that new emails from senders whose messages you've already starred in the past are not automatically starred as well. 

Gmail emails can be pinned even on mobile devices using the same approach that combines the Star or Important label with a non-default inbox view. However, stars won’t be added to future messages from the selected senders. For this, you will need to set up an additional filter rule in Gmail to mark messages as starred automatically when they arrive.