Pick a stack, then choose an open source project in that stack to contribute to. You can start by contributing docs and tutorials, then try to understand the co

Pick a stack, then choose an open source project in that stack to contribute to. You can start by contributing docs and tutorials, then try to understand the code base and fix small bugs. Work your way up to bugs and features with the most votes. That guarantees people are using your work, which managers appreciate. It also establishes authority in that software, which can lead to jobs if it's popular enough.