Ask HN: Whar are some productivity hacks you use?

I recently installed Chrome Extentions 3 Tabs (https://chrome.google.com/webstore/detail/3-tabs-only/pkfpaiidmiemediimekjfmlbhnbofabd)

Which only lets you open three tabs a time and hence forces you to focus only at the task at hand.

This plus I am new and learning GTD Method(Getting Things Done) with simple lists.

This two have greatly increased the work I do and also the speed of execution and also greatly reduced the stress level.

So now I am interested what HN, in general are using for great productivity (tools, techniques etc)