1) Base your self worth on something that doesn't change.
Examples: if you're spiritual: being a soul, being a child of God, being a "spark of the divine fire," or if you're not: being an organism on the planet, being a human being, being a humble warrior, being conscious and alive at this time in our mysterious universe.
Make a choice, then:
2) Deliberately put positive thoughts into your monolog. Examples: I'm so wonderful. I'm a terrific person. I have a good heart, and I mean well, and I'm learning all the time. I'm smart, and resilient. I'm worth an infinite amount. My birthright is to have a good life, and I can attain it. People love me the way I am. I have a lot to give. Failures are just stepping stones to success. Successes are stepping stones to greater failures. With the right skills, relationships are fun and nourishing.
At the same time:
3) Tag the toxic thoughts in your monolog, challenge them and replace them with the truth. Examples of toxic thoughts: I'll never be any good. I'm not worth anything. I'm not loveable. I'm so dumb. What a stupid thing to do. I can't do anything right. What's wrong with me? If I fail, I'm worthless. If I succeed, I'm worth a lot. If my relationship is going badly, I'm no good. Replace these with the thoughts in Step 2, all of which happen to be true.
1) Notice the ways in which you're acting as if you're inferior or unworthy, and stop doing those behaviors. Examples: apologizing more than once, making excuses, explaining yourself, settling, being shy, tolerating abuse, comforting the abuser, giving in, doing things you don't want to, avoiding, hiding, being depressed, not standing up for yourself, not following your dreams....
2) Act as if you have self worth. Examples: doing self care, being friendly, nurturing and assertive, defending yourself, negotiating for win-win, being loving, resilient and accepting.
Here's a version you can download: