I’m sSo pProud of mMyself

title case

I’ve been mtaking small steps to achieve my goal, which is defining the next action step whenever I find myself procrastinating.

"taking" sounds a bit more natural

I combined this with the next sentence, because that is how sentences starting with "which is..." usually are connected to independent clauses

Which is defining the next action step whenever I find myself procrastination.

And I takedo some simple experiments according to Ali’s book.

we often say that we "do" or "perform" or "run" experiments

I’m grateful that even when I’m feeling bad bout life, I’m still keep going.

I'm means "I am" so you could say "I am still not giving up" or something like that, but here "I still" sounds clear and smooth

I’m David Goggins, no one could stop me, don’t f**k with me.

this is understandable, but maybe consider the difference between

I'm David Goggins...(sounds even more intense perhaps)

and

I'm like David Goggins (sounds lighter and more casual)

I’ve been mtaking small steps to achieve my goal.

Which is defining the next action step whenever I find myself procrastinationg.

And I takedo some simple experiments according to Ali’s book.

I’m grateful that even when I’m feeling bad about life, I’m still keep going.

I’ve been mtaking small steps to achieve my goal.,

(1) The more appropriate word to use with "step" would be "take".
(2) I'd suggest merging this sentence with the one below. I have changed the period into a comma to allow for this.

Wwhich is definciding on the next course of action step whenever I find myself procrastinationg.

And II also take some simple experimentmeasures according to Ali’s book.

This flows more nicely from the previous sentence.

I’m grateful that even when I’m feeling bad about life, I’mll still keep going.

"Bout" is actually a real word in and of itself. If you want to use the slang contraction of "about", I'd suggest using an apostrophe to indicate this: "even when I'm feeling bad 'bout life". In very very casual situations like texting, however, you can omit the apostrophe.

I’m David Goggins, no one couldan stop me, don’t f**k with me.