Writing a new book on known methods/algorithms I am quite young but embarked on a rather new challenge for me: writing a book. There aren't so many books on this specific topic in my field: maybe 2 or at most 3 good references, with the first two quite old. The trouble for me is that although there is some clear original stuff in each chapter/section, the main reason for writing the book, the methods (some algorithms and numerical stuff, many equations) are quite standard and all good lecture sets (not too many) draw from these two books.

My book would be clearly better organized than the previous ones. However, the methods are basically the same. I mention that this chapter draws from x and y source, and sometimes that the theoretical part of a certain section is according to z source. 

Would citing my sources be enough in terms of not having issues with plagiarism?
Plagiarism is literally copying the text (or making only minor changes to pretend that you are not copying the text literally). Writing a book about something that is known is not plagiarism by itself, as long as you use your own words to explain the "standard methods".

If you do this, and if you do not copy figures and exercises (if there are any) it is not plagiarism. If you do need to copy a figure you usually need permission from the publisher (because of copyright, but that is a different issue than plagiarism).

So if your book has a different structure, is written in your own words, and cites the sources, it is probably not plagiarism. Your text simply needs to be clearly different from the original text(s).