Attend local gatherings or mixers. Local gatherings are a great way to meet both hobbyists and professionals in your area. It's also a good way to start building your network if you aren't a professional in the industry yet.
Attend conferences with industry professionals, such as GDC. Get to know someone first, then talk business when the opportunity arises. Networking at professional conventions can greatly improve your likelihood to get a business or career opportunity. You never know who you will chat with. They may be able to help you out in the future.
With the advent of social platforms, more and more people are establishing their digital networks on Twitter, LinkedIn, and Discord. Feel free to reach out to individuals on social media for advice and join Discord servers to interact with other hobbyists or professionals in a more casual environment. Don’t be afraid to ask for help. Contact professionals via LinkedIn or email. Get coaching or mentorship. Build relationships and help others. People will often help you in return.
You will probably meet lots of new people at in-person game jams. Or if they are online and have methods for pairing random people into teams, then you can network with your peers that way.