Interestingly you didn't recommend the most basic rule of craftsmanship: check (and replace if necessary) the tools you use. And with "tools" I mean tools! Your keyboard, your mouse, your monitor(s), your chair, your desk.
While none of the above will give you a breakthrough like that one super-productive morning which the gods shone their light upon, their impact will be small but constant throughout the whole year and the evaluation of their suitability requires nearly no technical skill at all. Just the willingness to pay for quality - exactly what you want from your customers too.
This one is really a key un-noticed one - get a wrist support for your keyboard and mouse, do you actually need a faster computer (or more memory) to speed up compiles, replace wireless LAN with a hardline LAN cable (more stable SSH, faster Internet with less interference), ergonomics can mess up energy levels too.
Do you need to upgrade that IDE or use the one you are more comfortable with ...
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