We spent some time trying to outline a systematic approach to thinking productively, stimulated by the mere title of Susan Stebbing's "Thinking to Some Purpose" (Pelican, London, 1939).
I suggested "Ten Obstacles to Clear and Productive Thought", as follows.
 Ignorance: in spite of the resources of the internet it is still a problem that most of us most of the time do not sufficiently know 'the facts'.
 Prejudice: we assume we know, and we often assume what we want to be true, which makes our error all the more difficult to rectify.
 Manipulation: we can be played upon by clever advertising, or 'hidden persuaders'.
 Potted thinking: we reduce an argument to a sentence, to make it easier to remember and express, even when the truth slips out with the detail.
 Ambiguities of language: it is surprizingly hard to say exactly what we mean, and to know what someone else means from what they say. Emotive language can pack a lot of argument into a single work (e.g. 'freedom').
 Logical slips: for example Post hoc ergo propter hoc, (or mistaking correlation for causation), and Petitio principii (or circular argument, which used to be called "Begging the Question" until that term got high jacked by the ignorant to mean simply "posing the question". 'Wise men give wise answers; this is a wise answer, because/therefore this is a wise man.').
 Attention span: we often drop a subject, or get side-tracked, before its goal has been reached.
 Conflict: is often avoided on emotional grounds when it should be welcomed on logical grounds.
 Circles: to find oneself repeatedly covering familiar ground suggest that the argument is being directed by a sub-conscious pilot.
 False syntheses: if repeated cases tend to illustrate the same general truth you have either discovered a valuable general principle, or a hobby-horse.