you just decide to think differently about everything, and really that's all there is to it. Make a decision of feeling better. You can choose what you think. Energy flows where attention goes, put your focus on what you would like it to be like instead of dwelling on problems.
Focus on what you DO want and repeat the appropriate affirmations over and over until it sinks in.
Also, it helps a lot to get physical movement in as well. Even if it's just brisk walking, make sure to move daily and you can repeat your good affirmations as you are walking and moving.
In a nutshell, you allow your feelings to flow through you and you build self love.
Start with going really general about your life. Like " There are so many nice things on this planet", "there are things I could appreciate about the Earth" , "Sun came up this morning, and I can enjoy light." Then get to something like " There are things, that go quite well in my life", "I have some things I can appreciate in my today". Then slowly you can get to more specific things you can appreciate about your life now. Whenever you feel not great, zoom out, and think more general.