In major casinos, you want to play machines that are visible from the isles, and preferably visible from the doorway. The management wants to have people seeing other people winning, to entice them into trying their luck.
You never want to play machines located in stores, or the airport. They pay off much more poorly.
All slots will take your money over time. One secret is to set a daily limit for playing and once you have spent that money,quit for the day.
If you hit a good payout (higher than your daily limit), take anything over your daily limit and put it away. Do not increase your limit because you have won, you will end up giving all your winnings back.
Remember, you most likely will lose. Only play with money that you can afford to lose, and look at it as paying for entertainment.
Life experience and I usually leave Vegas with about what I brought with me.