All of us preach a little.
I noticed on another thread you said working for perfection was a lie from the pit of hell.
That is preaching.
You don't have to be a "preacher" to preach. Preaching is simply telling someone something over and over again.
Perhaps... you have told someone to quit smoking. or quit drinking. or to quit looking at pornography.
That is preaching.
What Paul is saying here is.... ( my paraphrase)
I discipline my body... so that since I have told guys these things so many times... I won't be proving myself to be a hypocrite.
I've been telling you guys to do this... so I need to do it to. I need to practice what I preach so to speak.
Even telling our kids not to eat too much sugar, is preaching at them in a sense.
Of course we can also preach the Bible to others.