Bitcoin Core Development Contribution
Clone bitcoin core repo, build and test it yourself: https://jonatack.github.io/articles/how-to-compile-bitcoin-core-and-run-the-tests

Be active on https://bitcoin.stackexchange.com to learn and contribute

Experiment with bitcoin core GUI (qt) and CLI with different RPC commands mentioned here: https://bitcoincore.org/en/doc/0.21.0/ on testnet and regtest

Once you understand how things work, start looking for issues in https://github.com/bitcoin/bitcoin/issues that you can resolve or start with &quot;Good first issues&quot; with pull requests or create issues if you find something wrong while testing.

Participate in Bitcoin Core PR Review Club meetings: https://bitcoincore.reviews/

You can also start reviewing other PRs because bitcoin core has fewer devs to review a lot of code which delays things.

IRC channels that can be helpful apart from few technical posts on r/bitcoin, blogs of bitcoin devs etc.: #bitcoin-core-dev #bitcoin-core-pr-reviews ##bitcoin-core-gui