+You should set these variables. Here is an example of how mine are set in an init.el file.
+#+BEGIN_SRC emacs-lisp
+(setq reftex-default-bibliography '("~/Dropbox/bibliography/references.bib"))
+
+;; see org-ref for use of these variables
+(setq org-ref-bibliography-notes "~/Dropbox/bibliography/notes.org"
+ org-ref-default-bibliography '("~/Dropbox/bibliography/references.bib")
+ org-ref-pdf-directory "~/Dropbox/bibliography/bibtex-pdfs/")
+#+END_SRC
+
+You may want to set some convenient keys for working in your bibtex file:
+
+#+BEGIN_SRC emacs-lisp
+(global-set-key [f10] 'org-ref-open-bibtex-notes)
+(global-set-key [f11] 'org-ref-open-bibtex-pdf)
+(global-set-key [f12] 'org-ref-open-in-browser)
+#+END_SRC
+
+ Change into the directory you cloned org-ref into and run this command to generate the elisp files.
+#+BEGIN_SRC sh
+make tangled
+#+END_SRC
+
+Add the directory you cloned org-ref into to your load-path, and require the features you want.