Other MMOs have some form of panel, window, or board that allows players to locate other members who want to adventure together in dungeons or instances. RoM's recruitment board is accessible on everyone's screen by clicking the appropriate button. Players can join groups and create customizable searches based on class, level, dungeon, and other requirements. It never gets used much, but it's definitely not a useless feature.
Chat seems to be the preferred method when looking for a PUG. It's an old-school way, but the fact that anyone can see your message in his already-useful chat-window makes it efficient. Although RoM players tend to be spread more evenly between zones than in an MMO like World of Warcraft, that has players all going to the same zone to take care of business. The world-chat function also costs you in megaphones, so if you're being frugal about using megaphones between selling your items and spamming for group members (or if you don't use world-chat at all), you may want to consider utilizing the board. It can be to your advantage to simply recruit from within the zone containing dungeon you want to explore, but not everyone who's willing to join you will be in that zone. I don't know about you, but for me the trade-off of free zone-chat doesn't always seem balanced with the time it takes to go through all the different zones.
Make life easier
Players who have experience with raiding in other MMOs know that it can be a full-time and time-intensive activity. Whether you group with guildmates or find PUGs, it can eat up a lot of time, and that's before you even start the dungeon. Making a habit of being prepared shaves a lot of time off everyone's waiting period and saves you the embarrassment of making the other players wait while you take care of last minute preparations. You don't have to have a bank overflowing with health and mana potion, but it pays to find out the time involved in any instance you're running and stock-up accordingly, before you agree to meet at a dungeon's entrance. Always remember to repair your equipment before going into an instance, too.
RoM doesn't have a dungeon finder, but it does have teleport runes that allow you to mark locations for instant travel later. If I added up all the time I spent running to Necropolis of Mirrors, or first running to a teleport to Silverfall, it'd probably be many hours. Marking a location right next to the entrance saved me travel time to start the dungeon, and it also allowed me to quickly get back in when I died and had to resurrect outside at the nearest resurrection point.
Good etiquette is good etiquette
Tackling a dungeon as a guild tends to have advantages over pugging. Chances are you will have played with guildmates long enough to learn how to work together as a well-oiled machine; there's usually a clearer understanding of the loot everyone expects to get and what everyone needs from any dungeon; and most items, whether junk or not, are shared between everyone to benefit the whole guild.
Loot rolling is something that's important for all party members to understand and agree on before going into a dungeon, especially if you're in a PUG. If the group doesn't decide what everyone will roll need on and what everyone will greed on, it could create a lot of animosity. It can be hard enough finding a PUG when no guildmates are online, and you don't want to have the added stigma from being known as a ninja looter.
Whether I'm with guildmates or strangers, I always like to be on the same page as to how everyone will be rolling for loot. There's always some wiggle-room for how your guild operates, but more times than not, guildmates will happily dole out items evenly, pass on items they know your class can use, or simply pass on items to be nice. Many people extend this olive branch when joining a PUG, but they shouldn't expect the courtesy to be returned.
You might handle courtesy in PUGs differently, but I tend to be fairly strict. When I'm with my guild, I always talk it over and decide who needs what, beforehand. I also try to communicate with everyone in a PUG, but questions can go unanswered while everyone anxiously jumps into an instance. If I'm still unclear as to how everyone will be rolling for loot, I will feel out the situation within the first few battles. If I don't feel comfortable with how to roll for loot, I fall back to my rule: always roll need with strangers. This, of course, doesn't always mean I will roll need for everything. I can still courteously pass on items that will only carry a moderate gold value, but anything that is really valuable -- regardless of whether it's for my class or not -- I will roll need on.
Try to learn how to effectively play your class. Even though it's reduced in dungeons, XP debt is accrued by everyone when he dies. It doesn't really make finding a PUG harder, as raiding is a pretty big feature in RoM, but debt does make the desire to stay alive greater. If you're obviously jumping around care-free and aggroing every mob in sight, you will not make a good name for yourself, and it will be harder to find future PUGs when you want them.
Don't dismiss the recruitment board. It can save you megaphones and work in conjunction with the chat channels. Don't wait until everyone is standing outside a dungeon to prepare for it. Repairing armor and stocking up on potions in advance will save time. If you have them, you can use teleport runes to instantly warp to a previously marked area outside of dungeon entrances. Play nice, play fair and everyone will have more fun. Good etiquette goes a long way in any dungeon you're running, and will convince people you're a good person to come back to for future grouping. Finally, be mindful of XP debt. Not all players have easy access to a God's Redemption Ticket or a guild library to quickly remove any debt they accrue.