There isn't actually much difference between the two sentences. I would say the first sentence is just slightly less formal than the second. This doesn't mean that one of them is right and the other is wrong, and I would not say the meaning of what you are saying is different in either sentence

The first sentence implies a process taking place - I'm going to write good jokes, and this will lead to my becoming a comedian. In the second sentence, the comma separates the two actions, and so they are no longer as connected - I'm going to write good jokes, and independently of this, I'm also going to become a comedian.

The second on is more like you are positive that you will become a comedian while the first sentences the steps or process of becoming a comedian or how you will become a comedian.