I usually wait 5 years. If the tech is still there (and it's stable) and devs are using it, then I start learning it. > The real question is how you decide whe

I usually wait 5 years. If the tech is still there (and it's stable) and devs are using it, then I start learning it. > The real question is how you decide where to invest your time/energy next? Just learn whatever you think it's fun. It's not that you are going to learn 1 single tech in a whole... decade? I usually spent around 3 months with new tech. That's like 3 or 4 new techs per year, so don't worry about picking up something you like that is not that much relevant in the industry. Also, playing around with something for 3 months is enough for applying to jobs that require such tech (only if you have solid fundamentals, otherwise work on them!)