Block early, block often - people are not always nice on the internet:-).
There are many unwritten rules. One is that Lemmy.ml will ban you for saying anything critical of Russia, China, or North Korea - but they won't tell you that straight-up, you are somehow supposed to "just know".
Likewise on midwest.social you can be banned for downvoting a post or comment by the admin. Most admins are not that way, but that one is.
If any of that sounds bad to you then you may want to avoid communities on either of those instances.
Lemmy.ca though is a very nice instance - good choice:-).
You might also check out PieFed - it hasn't caught up to having as many features as Lemmy yet, but in many ways it has already surpassed it, and in particular the categories of communities can help you find communities to subscribe to with your lemmy.ca account.
Browsing by Local on Lemmy.ca is another great way to find communities that you may like. Also you can click the Communities at the top of your page, make sure it is set to All, and search for what you are looking for across the entire Threadiverse. Those stats can be misleading though, as sorting by total users disregards people that have abandoned old communities (especially happens on lemmy.ml and lemmy.world) but without "unsubscribing" - "Active Users" is a better metric, or just click each one and you'll quickly see how active the community is.
Welcome to the Threadiverse!:-)
