My top 3, in order of how I try to apply them (i.e., if 1 doesn't help, move on to 2, etc.). I learned these all from reading various philosophy works, by the way, so perhaps cognitive hack #1 should be "read books".
1) Suspension of judgement (from Sextus Empiricus, Zhuang Zi, Ecclesiastes): avoid forming an opinion at all about things that are not evident. The way I do this is by thinking through an opposing argument or two, and using language like "it seems" or "it appears" rather than "I know", "I think", etc. This technique saves time and energy by helping me avoid getting wrapped up in opinion-based thinking and helps me develop equanimity.
2) Suspension of value-judgements (from Epictetus, Marcus Aurelius, Seneca, Zhuang Zi, Ecclesiastes): being aware and in control of the value-judgement loop (this thing is good or bad). I do this by shifting the language in my mind from "that is bad" to "I feel this way because..." Again, like #1, this is about inverting the locus of control in my cognitive discourse such that my mind can easily go its own way from there, only on a more productive path.
3) Awareness of the mode of thinking I'm in, and the kind of learning that's appropriate to the task or objective at hand (from Plato). There are several modes of thinking or learning (eikasia, pistis, dianoia, episteme, techne, phronesis, and noesis, for example). Simply being aware of which mode you should be in for a task is much more valuable than it might appear at first glance. I see these less as bins to put various kinds of thought in and more as tools to apply to a problem.
Reviewing this, a common thread is self-awareness developed to a point of disciplined introspection and intentional change by adopting these kinds of cognitive tricks. Also, reading is good for you. :)