The simplest way to get involved is to start attending the biweekly standardization meetings. The agendas are organized here: https://github.com/WebAssembly/meetings
To attend the meetings, first join the W3C WebAssembly Community Group here: https://www.w3.org/groups/cg/webassembly, then email the CG chairs at webassembly-cg-chair@chromium.org to ask for an invite.
From there you'll get a sense of who folks are so you can pair names with faces when contributing to the various proposal discussions on the many proposal repos listed here: https://github.com/webassembly/proposals.
To get a sense of how things are run and decided, read the process documents here: https://github.com/WebAssembly/meetings/tree/main/process. The TL;DR is that the community group and its subgroups decide everything by consensus via votes during the meetings.