While interrogating the theoretical assumptions, as John Lye puts it, one ought to be aware of the difference between Literary Theory as a subject, and theory itself.
Literary Theory is, as Deleuze and Guattari remark in Mille Plateaux, an arrangement of ideas within a demarked space: one has the author, the reader, the text, society, etc, and a theoretical position will articulate the importance and the nature of the various relations among them. This is disciplined and disciplining theory, theory ready to hand for the practice of literary criticism, theory as practiced and approved by the regulatory bodies of the 'discipline.' One then has a 'theoretical position' from which, or through which, one acts, as a 'reader-response' theorist, or a 'psychoanalytic' theorist, or whatever.
Theory Itself, on the other hand, is always one step off, is not to hand for criticism, because it is attempting to assess the assumptions and implications of the demarked space (why it is demarked, by what process, what the demarkation suggest, on what grounds and for what reasons these are authorized, and so forth). The practice of theory itself is self-reflexive, for it includes an examination of the grounds of one's own practice, authority, and goals.
