The best-ROI techniques I've found to date are getting sufficient sleep, and trying hard. I know that these work, andthey work quite reliably.

Another which is somewhat less reliable is 'sleeping on it.' I mean quickly and intensively priming the mental pumps on a task, then doing something else, then coming back (ideally after a good night's sleep) to the task later. I often perceive the benefit of signicant effortless processing which must have taken place in the interim,

Back to trying hard. To help w/ this, I tend to psych myself differently depending on the mental barrier of the hour, e.g. (just by way of example):

raring to go -> go (duh); low energy -> compete with self / make it a game / hyperoptimize; anxiety concerning outcome -> depersonalize, take cosmological perspective, dust-mote-on-dust-mote, etc.; self-doubt -> reflect on successes and known abilities, depersonalize; lazy -> see low energy; competition for focus -> promise self rewards if focus, quick-list competing demands then flush from mind, etc.; uncertainty - 80/20 rule, do-then-adjust, countless pithy sayings

The psych-up phase may take 5 seconds (most of my techniques are so familiar I just need a quick flash on them to get most of the effect). Ideally I've planned ahead sufficiently so that 'sleeping on it' is still an option if I feel insufficiently psyched after the psych-up phase. Sometimes, just reminding myself of this fallback makes the psych-up easier.

Fairly mundane stuff, but reasonably effective and equipment-free (the bed I'll be needing anyway:-)