I'd start with putting vending machines and putting them in police stations (obviously pay your dues on this one). My friend does that and he says those are always his biggest money makers, since a police station is essentially open 24/7 and the foot traffic is extremely interested.

I'd say if you can make money with vending (I presume the machines depreciate much slower than video games), then move on to experimenting with a few games.

Nate