Twenty-two affirmations for looking in the mirror — to say to your own face, which is harder and works better.

Saying something kind about yourself is one thing. Saying it while looking at yourself is a noticeably different experience, and most people find out very quickly which of their kind statements they actually believe.
These twenty-two affirmations are for the mirror specifically. Say them to your reflection, out loud, and hold eye contact for a second longer than is comfortable. The discomfort is the part that changes.
Start with eye contact and nothing else. Thirty seconds of just looking, before any words, takes the edge off — most of the flinch is about being seen rather than about the sentence.
Then choose lines you can nearly believe. "I deserve to feel good when I see myself in the mirror" is reachable on a bad morning in a way that "I am in love with the person I see" may not be, and reachable is what gets repeated.

1. “I am in love with the beautiful person I see in the mirror.”

2. “When I look in the mirror I find beauty.”

3. “I am filled with excitement when I look in the mirror.”

4. “I look in the mirror and say, "I love you".”

5. “I see confidence when I look in the mirror.”

6. “I see only good qualities when I look in the mirror.”

7. “I am proud of the body I see in the mirror.”

8. “I adore the person that I see in the mirror.”

9. “I see only the positives when I look in the mirror.”

10. “I admire the person I see in the mirror.”

11. “I see nothing but reasons to be happy when I look in the mirror.”

12. “I see a person with limitless potential when I look in the mirror.”

13. “I am happy with the amazing person I see in the mirror smiling back at me.”

14. “I see a spectacular human when I look in the mirror.”

15. “I adore what I see when I look in the mirror.”

16. “I appreciate what I see when I look in the mirror.”

17. “I see beauty and grace when I look in the mirror.”

18. “I feel great happiness when I look in the mirror.”

19. “I am in love with the amazing person in the mirror.”

20. “I deserve to feel good when I see myself in the mirror.”

21. “It feels good to look in the mirror and love what I see.”

22. “I see beauty, power, and strength when I look in the mirror.”
Because it removes the escape route. You can say something kind about yourself in the abstract and not really apply it; in front of a mirror it is unmistakably about the person standing there. The discomfort usually eases within a week or two.
One to two minutes is plenty. Longer sessions tend to turn into scrutiny, which is the opposite of the intended effect.
Pick a smaller line. Belief is not required for the practice to work, but total disbelief makes it unpleasant enough that you will stop, so aim for the ones you can half-accept.
Self-compassion practices have reasonable support for reducing self-criticism and improving body image, and mirror work is a concentrated form of one. It is a practice with a decent record, not a cure.