Corrections are in red.  Suggestions to make it sound better are in blue.

There's a grain of truth in every joke.

It is a Russian expression. It means that when you are joking, in a deeper sense you are expressing a bit of the truth. I am a beginning writer. Correct me.  And what do you think about it?

I don't think that every joke contains a morsel of truth.  However, the funniest jokes often do.