I've added a police station, a gym, and a cinema specifically because those are supposed to help you curb the crime in your city. I still seem to deal with a fair amount of it, but I could stand to get more of everything. I'm putting some Hive into it, but I don't want to go crazy spending on a game.
Aside from that, a large focus of mine is just adding workers as often as I can. I'm trying to add buildings and add workers at a somewhat equal pace so that I never end up too far out-of-balance.
The amount of SIM I earn seems to go consistently go down if I don't keep adding, though. It would be tempting to maybe just let the SIM accumulate and spend that building the city, but that would result in a glacial pace.
Yesterday, I found some SBD (Steem backed dollars) in my Bittrex account that was locked since late 2018. It was only like 3 SBD, but it ended up being over 80 Hive by the time I was done with it. I put a lot of that into dCity, but not all of it. I'm playing other games as well! I bought a few things for Rising Star, which I'm playing as 
So far, posting pretty consistently about Rising Star has been the best thing I can do as far as earning some modest amounts of HBD is. To be fair, though, I don't post as much about this game because it doesn't seem as obvious what I can make updates about sometimes.