The only way to reliably win it is to complete quests to open up more spaces for reels on your slot machine, then to fill those spots with reels that give you a high statistical probability of matching a certain attribute (or wild card).
For instance, each place you can whore statistically favors a certain type of activity. On the pirate ship it's Hand Jobs. It just so happens, not by coincidence, that you start off with reels that favor that and that Julius will occasionally sell ones that are a direct upgrade by providing a bonus wildcard slot (I believe, it's Perversion) or a common wildcard reel which is more balanced in sex acts, but has 3 wildcard spots on it.
The game is designed to be lost a lot when you first start. You should be burning through Willpower at a decent clip until you unlock at least the 1st slot and then upgrade your reels (completing the quest gives you an upgraded reel as well). In addition to that, in order to get the best outcome in mood raising, you need to completely 'satisfy' a customer. Which means usually matching on them 2-3 times at the beginning of the game when your skills are low (skills actually matter and gain xp during this game). The best strategy early on is to horde your energy by resting most of the day, then whoring only at night, until your skills improve and you gain some slot upgrades.
You can buy additional reels from brothels, assuming you increase the favor with their owners by doing their jobs/quests. These reels are all specialized in a single sex act, so they can be powerful depending on which area you are whoring at (matching a sex act directly, without wildcards, gives you the most money and xp). Reels will also show up randomly in the Bazaar and Market if you shop there. Of course, some quests also give the reward of free reels that may or may not be useful depending on what you're aiming or.
So, the game, while being 'completely random' isn't really random at all because you can go out and acquire new reels and swap them in at any time during play, more or less making all the odds significantly stacked in your favor.
Finally, version 0.10, which is in development, has the addition of a new game 'Coffin Dice' - a simple dice game where you can place bets for money or items with the pirates. You can also occasionally bet a sex act (if you lose, you pay with sex). The amount this covers is based on your skill, but it presents an alternative way to gain money and sex skill xp, although it doesn't scale as well as the slot machine game does. It's unlocked after a special event on the ship.
