It's totally random...sort of. What you do is this: You sit down at a slot, or you sit where you can reach three machines, and you start feeding it or them. When the cocktail waitress comes by, be nice to her. Tip her if you order something from her. When the slot machine tech comes by--to make a payout or empty a machine or something--be very nice to him or her, but don't be a kiss-***. Stay at your machines for a while and get to know the casino workers assigned to your area. Talk to them about interesting stuff--but don't be obvious and fawning. Be patient. Play your slots, do your thing, take it easy. Eventually, if the waitress or the machine tech likes you, they'll tell you which machines are due for a big payout. Once they give you that info, give them a nice big tip, move your *** to one of the machines that is "pregnant" and ready to give birth to a whole bunch of change, and play that one. If it doesn't hit that night, go back to it tomorrow, after learning from the waitress or tech whether it hit after you left yesterday.
Apart from this, there are no strategies or techniques. It's totally random, as I said.