Comment by cornel_io

Eh, there are a few language-specific gotchas, but if you're good at optimization it's really nothing too tricky to figure out within a few weeks. The core problems are the same, depending on the class of language: far from the metal, allocations and GC are almost always what kill you. Close to it, cache misses.

Beyond that, it's just making sure you do less stuff, and being really aggressive with profiling (what looks like it takes the most time in the code almost certainly isn't what's really taking the most time).