Also, one last thing I'll mention is that unlike Mastodon, relays here are not federated, so they don't communicate in between each other unless it's specifically set up that way. 

So in a way the relays you're connected to do matter for the content that you're seeing. I imagine if Nostr really catches on there will be topic-specific relays like sports or whatever. But for now And it kind of sucks to say this, especially from a decentralization standpoint, but connect to a few smaller relays and then make sure you're connected to some of the larger relays and you generally won't have a problem with people seeing your stuff.