Can I publish research from conference proceedings?
There are different types of conference proceedings that are published. Sometimes, the conference proceeding would only include an abstract and sometimes it could include full length papers in the form of a journal. If you have published such a full length paper, it would not be appropriate to submit the exact same paper to a journal.
However, if only the abstract was published as part of the conference proceeding, you would be eligible to submit the paper to a reputed journal. However, at the time of submission you need to mention about the presentation of this work at a conference earlier in the cover letter. Sometimes submitted abstracts are indexed by google scholar and could be picked up as self-plagiarism by journals if the editor is not informed about the submission to the conference earlier.
Also, in most cases, work presented at a conference is usually work that is in progress and in not complete. And discussion of such work in progress at a conference could be considered as an effective way of getting your work peer reviewed before actually submitting it to a journal. Useful comments/suggestions if received can help you improvise the quality of your work and your paper. In such cases, the final paper that you would put together will always have additional or improvise data/information in comparison to what you had presented at the conference. This paper which would be an extension of what was previously submitted cannot be therefore counted as a duplicate submission. However, as mentioned before, you would have to mention to the editor that a part of this work was presented before. If possible also check for the journals policy regarding such submissions, in the author instructions on the journals website. If this information is not available, you could also send a pre-submission enquiry to the editor before going ahead with the submission.