Build your partner up with words of affirmation.

When your partner does something you appreciate, let them know.
It could be as simple as telling your partner you appreciate it when they take the trash out. Verbal compliments will make your partner feel loved.

Make a list of all the things you like about your partne
Continue to update this list whenever your partner does something you appreciate. Refer to this list for ideas on what to affirm your partner about.

Use kind and humble words to express yourself, and encouraging words to speak to them.
Instead of attacking them when you have a disagreement, focus on letting them know how you feel - stressed, hurt, disappointed, etc. Similarly, when they do something right, encourage them on!

Indirectly affirm your partner.
Tell others how much you love and appreciate your partner. Eventually, someone will tell them and you will get full credit. You can also write down words of affirmation in a letter for them to read whenever they feel down.

Keep a written record of all the words of affirmation you give your partner.
This will help you keep track of whether or not you are affirming your partner sufficiently. You should aim to give your partner a different compliment at least once a month.