depends on a lot of things. neighborhood type, "quality". proximity to arterials, property layout, etc.
If you put up a fence to reduce people entering and crossing your property from all directions, and your building is in an area that has graffiti or street crime issues, make sure its a chainlink fence, or a low one, or otherwise not an "attractive nuisance" that invites tagging or can hide undesirable activity. Prickly hedges take a while to grow but work great for that. You cant tag plants.
Good automatic (combination of motion and night sensing) exterior lighting is worth a lot. Make sure there are no overgrown trees/bushes people can hide behind.
Be quick and proactive about cleaning up trash and graffiti/etc if an issue, the whole "broken windows" theory does have some merit and besides good tenants will appreciate it.
I use a simple security camera system aimed to cover parking area and common accessways to one of my buildings, but explicitly NOT aimed at individual unit entrances. Its capable internet connectivity though I'm running it standalone. The DVR recorder is well hidden in a corner of the crawlspace so unlikely any creeper would find it. I put a monitor in the laundry room so tenants can see what it sees and confirm its working. Building is on a low/moderate busy arterial and that cut down car prowls and trespassers probably 60-70%. Still, I've got great video of a pair of people walking up to a tenants car, pointing at the camera, then taking about 120 seconds to break into and drive away with the car. No security system is perfect.
Maybe replace coin op laundry machines with card operated or some other cashless type to dissuade breakins and theft there. Social engineering is worth something too. Even if you do have coin op machines, maybe hang a "did you forget your laundry card?" sign on the door. Little lies sometimes are helpful.
If there are common entrances separate from unit entrances they may need to be lockable too, and make sure they have automatic door closers and tenants don't prop them open.
Ring cameras or similar for tenants?
Of course you can also have a full blown commercial security system for each unit. I've never had such a system so I have no opinions on cost