[drtse4]

0. Fix your algorithms, code optimization comes later

1. Avoid abstraction as much as possible, convoluted flow control and reduce useless objects creation

2. Learn how to manage concurrency correctly, focus on the data being accessed by multiple thread and focus on sequential access

3. Don't use bloated frameworks (all of them)

4. Consider rewriting common libraries following the principles above and with only the functionalities you actually need.

Easy 10x improvement, try it.