Speak in the present tense.

Don't say:
"Next year, when I have more clients, I will earn more money."

You must create a vivid picture in your mind. 

Say instead:
"I have a steady stream of clients."
"I'm attracting abundant income into my life."
"I'm receiving financial rewards because I provide immense value."
"My worth is so great that I confidently charge what I deserve."
"My belief in my value frees me to earn the money I want."

Use words that excite the imagination.

For example:
"My financial abundance exhilarates me, it uplifts me, it empowers me, it sets me on fire. It gives me the motivation and energy to pursue all of my financial goals."
Words like these help your mind to visualize your success.

Avoid using the words 'No' and 'Not.'

For example, don't say:
"I'm no longer undercharging. I don't feel unworthy of abundance. I'm not afraid to ask for what I deserve."
"I'm no longer worried about money."
"I'm no longer stressed about my finances."

Note: "I'm not..." doesn't create a vivid image, but "undercharging" and "worried" do.