It’s not at all important to get it right the first time. It’s vitally important to get it right the last time. (Andrew Hunt and David Thomas, “The pragmatic programmer”)

This is a corollary to “Proofread and double-check your paper before submission“.

If you are still finding typographical or other errors in the paper while reading it, or if you are still adding results and commentary to the paper, then it is not yet time to submit the paper to a journal.

Even if you are for some reason in a hurry to publish your paper, a poorly prepared paper will have a greater chance of rejection, may incur demands for major revisions, and will in general slow down the processing of your paper to the extent that it would have been faster to wait until the paper was in a more final form before submission.

For similar reasons, if you are sending a copy of your paper to a colleague, it would be considerate to send that colleague a version of the paper that already has been proofread and to which a significant amount of work has already gone into improving the exposition, rather than an early draft which may take up more of your colleague’s time to read.