I am a final year PhD in UK in a scientific discipline and I am writing my thesis. I have already published 2 journal papers and I have submitted 2 more papers for publications. My department does not allow a "publications-based" thesis so I need to write a thesis in the context of a book etc.
As I write my thesis in a couple of places, especially in the literature review, I tend to reuse sentences from my publications. I try to restate them a bit, maybe change some words for their synonyms etc. but it is practically me writing about what I wrote before. It goes without saying that I cite/quote me at the end of a passage if I say something non-obvious (I found that slightly funny. :) ). The problem is that occasionally I am just explaining for instance how a certain estimation technique works; in that case I cite the original authors and not myself. The syntax in those occasions though is practically the same as the original passage I used in my publication; as I have explained it once and was consider good, I find no reason to reinvent myself (I do a mild rewording as I mentioned but that is quite insignificant). Same things goes for listings. I do cite my paper in the beginning of a big list as the list's source but the list itself is almost identical as the one in "my" paper; in those cases I don't use quotations, just attribution "[]".
Is there an obvious guideline? The basic definition of plagiarism "reproducing the work of another person's as your own" is not (directly) applicable to me because I am the other person (almost *); if I am using other people's work I do cite them but I don't cite myself, citing them, in quotation marks!
I am a bit "fuzzy" about how not to plagiarize myself in my thesis (I have had no problem regarding my journal publications).
(* In all publications mentioned I am the first -but not sole- author.)