Some practices that could hurt your FB algorithm
1-Joining lots of groups you can't engage in.
You only need a little number you can engage meaningfully with their contents and not those you will have to mute or keep ignoring notifications from them.
Also stay away from Markets groups where everyone goes to promote their stuffs especially those groups where people spam one another. You may also be marked spam
2-Adding too much friends you have nothing in common with. You will keep skipping their posts and they won't also engage with yours.
This will affect your reach as you will end up adding a bunch of inactive friends as many people will not see your post due to lack of engaments.