In general, always play the maximum coins. It is difficult to find a machine that doesn't offer a bonus on the highest hand for five coins played. If you are uncomfortable playing five coins then drop down to a lower coinage.
The cards are chosen at random. There is no switch inside the machine that can make the machine loose or tight.
A royal flush can come along at any time with equal probability. A machine is never "overdue", so it follows that it becomes more likely to hit. Theories such as that a machine will get very tight right before hitting a royal are simply not true. Given no change in strategy a royal is just as likely to be hit right after the last one as a million trials since the last one.
Always use a slot club card if there is one, and there usually is. This is free money for playing and can often make the difference in having an edge or not.
Do research on where the most generous machines are.
Video Poker Acronyms:
AA: All American Poker BP: Bonus Poker CPH: Cost Per Hour DB: Double Bonus DDB: Double Double Bonus DDJ: Double Double Jackpot DW: Deuces Wild EV: Expected Value FH: Full House JB: Jacks or better JW: Joker Poker Kicker: A 5th card that increases the value of quads LD: Loose Deuces RF: Royal Flush SF: Straight Flush