There are different ways to say it. In speech, we might say: - (자, 이제) 농담(은) 그만하고, ... (then switch to the serious subject) - (자) 농담은 그 정도(로) 하고, 이제 심각한 얘긴데 ... * 농담 = joke. You could also say 우스갯소리, 우스갯말, 웃자고 하는 말, etc. In writing, you can say the above or something a bit more formal. - 이제 농담은 그쯤하고 본론으로 들어가면 ... (So much for jokes, and moving to the real topic, ...) - 그건 웃자고 한 얘기고, 이제 본론입니다. (That was a joke, and now I'll get to what I really wanted to say.) * 본론 = the main subject.