Show them unconditional love. Tell them that you are always proud of them. They shouldn’t need to get good grades to earn your love.
Let them be curious. If they’re into something, make that thing seem important to you too. If they ask questions, no matter how silly they are or how many there are, encourage them to ask more. At the very least, don’t get annoyed when answering them.
Teach them that it’s ok when things don’t go their way.
Teach them that honesty is key, but if they can convey their honest opinion in a nice/respectful way, always opt to do it in that manner.
Be supportive, but not overbearing. Let them fail, but step in before it’s catastrophic.