There’re many common mistakes to be made when designing, but here are a few that may be less obvious.
One common mistake is designing for yourself. It’s easy to default to what you like, but most often you’re designing for a client and/or target audience, requiring sensibility for their appeal over your own personal taste.
Another is not including or adequately emphasizing visuals to grab attention and convey the message instead of just text.
Finally, it’s easy to overthink when designing, leading to self-censorship of creative ideas and adding clutter that distracts from the message. Remember to keep it simple.