Any slot game online has some "hot" and "cool" periods. This means that the machine would give you some earnings for a few spins, and then it would make you lose in order to claim its winnings. If you want to play smart taking advantage of this fact, you will need to follow the slot machine:
Play with a low stake for a few spins. If the slot machine gives you winnings for two consecutive spins, it means that the machine in hot. Increase your stakes and play for 10 or 20 hands. Again, if the machine won't give you any earnings for 5 or 6 hands, it means that the machine is getting cold; therefore you must lower your stakes or leave it.
The strategy has many variations also.
Considering the machine and the casino, you could try to play more hands, even if you are losing. Some machines have longer "cooling" and "getting hot" periods; therefore, you must play longer in order to determine the state of a certain machine. Some players are also saying that you must leave a slot machine if it gets cold, as it would take a longer period to become hot again.
Create your own strategy based on the denomination gambling strategy. Watch a certain casino, see the trends, and create your own betting style. After all, those are only general guidelines and the ensemble must be determined only by you and your playing style.
Take advantage of experienced players
Some advanced slots players always have a list of excellent slots machines that are always hot. Of course, you will have hard times finding this kind of player, and about convincing him to give it to you. If you find such a player, you could propose him a partnership: ask for the list and give him a part of your earnings. However, take great care, as the casinos are not so comfortable with this technique. Moreover, they are entitled to cancel any winnings if this kind of partnership is proven. Speak about those strategies on external channels such as mail and Skype, and don't use the casino chat to close those kinds of "Deals."
This is more like an advice than a strategy. A player that loses many hands consecutively will become anxious and nervous. He will start to gamble more, hoping to get the lost money back. This is a huge mistake: if you lost 15 % of your total bankroll in a single night, you must call the day off. You will surely get that money back once your winning spree is back.