There is no such thing a perfect Dungeon Master.
Some are great ones, some good, some down the line, but there is no DM so skilled as to need no improvement.
In fact a DM can regress by laziness, repetition and too much self-confidence.
Therefore the key focus is how you can get a better DM.
There you can find some suggestions which will help you to countinously improve yourselves.
Refresh and change
Laziness is terrible for a DM.
If you continue to submit to your players the same kind of adventures or campaigns, not only they'll grow up bored but you won't improve, remaining ever chained to the same mechanics and situations to solve
Change adventures type from time to time, and test yourselves in new challenges: it'll be satisfying not only for your players but even for you.
Learn from others
Watch other DMs and players.
You can learn a lot from their examples.
You can get new tricks to run a game or some inspiration to create a new campaign.
Listen to your players
You should listen both suggestions and complaints.
Many good idea can come from tyour players: after all they're the first-hand witnesses of your work.
Their ideas can lead you to new better ways.
Read the rules
A DM must know the rules.
Many don't know them, I've seen, or after have forgotten or twisted some of them.
Periodically re-read the Player's Handbook and the Dungeon Master's Guide.
You'll find everytime some bit of informations you had previously missed or misunderstood.
Make yours these simple suggestions.
They'll help you on your quest to improve as a DM.