If you really want to, first do a metric shitload of legal and commercial prep work, including picking a specific ISP for the exit node, registering an LLC or equivalent to be the legal entity that owns the exit node, and all sorts of steps that mean when the inevitable deluge of traffic from hackers, bittorrenters and so on come through your exit node, you're at least somewhat insulated from the blowback you'll get. Prepare for answering legal queries about your exit node being your full time job.
Read https://blog.torproject.org/tips-running-exit-node/ first, and note that even that post is 8 years old.
If you merely want there to be more Tor exit nodes in the world, I recommend you donate to an existing operator of them, like https://torservers.net/ -- if you read their blog, https://torservers.net/blog/ , you'll see the latest entries (also from 8 years ago) are about seized servers and arrested operators.
If you want to donate your ISP bandwidth for improving the Tor network, do it by running a guard relay or middle relay, that is relatively straightforward.