Q: I want to cite my previous paper to clarify that it is not a double submission
In order to clearly show that my manuscript is not a duplicate submission, I want to cite my previous paper. Which is better to write it in Introduction section or Method section? Or should I mention it in both sections to emphasize it?
Yes, it makes sense to cite your previous paper if you are expanding upon it or referencing it in the current study. Regarding where it should be cited, that would depend on what part of your study you are citing. If you are talking about the aims of your previous research or summarizing what was done under that, you can cite it in the Introduction section, and if you are talking about the methodology used, you can do that under the Methods section and cite it there. The idea is that the citation should be placed right next to the part of your previous paper that you discuss in the current study.