Mare Sacro Monastary (MSM) is the first "Group" Adventure, ie 5-man dungeon, you'll gain access to as you progress in prestige in Skyforge.
Like most areas you gain access to for the first time, Skyforge seems alright with dumping you right into an Impossible rating version of the dungeon--don't do this if it's your first time and be sure to manually drop it down to a lower-star difficulty to get your feet wet. Group Adventures in this game are no joke and will wreck unorganized random groups, so you want to take the challenge at a reasonable pace your first couple times.
Entrance
Going in, the first several pulls are primarily groups of swarm mobs. They're not difficult to handle but CAN do damage quickly so be prepared to pop shields. Also, beware as you cross each bridge, as 1-2 kelps will jump up along most of them.
1st Gate
This pull can be pretty serious and is where most unprepared groups are going to hit a wall. The swarm mobs need to go down ASAP but targets after that are a bit of a crapshoot.
Icy Abyss Kelps hit hard and will pursue the tank in melee range. On occasion, it will pull in all nearby players and then create a bubble around itself which will burst, damaging players nearby after a short delay. Everyone pulled in needs to get away from it quickly.
Roaring Waves Naiads are simple ranged enemies. They can be kind of LOS'd behind the planters visible in the above screenshot, but they may path right up onto them.
I would recommend the tank grab all mobs and kite the Icy Abyss Kelp. I would also recommend killing it first before the Naiads to simplify the encounter but any order is mostly fine.
Labyrinth
The next area has this kind of grid-y layout with groups of enemies at each corner of the yellow triangle, single kelps scattered throughout, and 3 patrolling Icy Abyss Krakens. 2 of the Krakens patroll each of the vertical lanes and one patrols east-west across the middle-top lane.
Make sure, before pulling any groups and while fighting, that you are aware of where the Krakens are so that you don't pull them also. When and if you can pull them safely, they only take a minute or two to take down. I usually grab the horizontal one and then one of the vertical ones to have a clear path.
Incidentally, the Krakens actually do eventually respawn if you spend too much time in the area.
I usually pull this west group first and, as you can see, from the west corner (as opposed to a lot of groups that like to pull them towards the gate). This gives you a LOT more options for LOSing them for the pull and breathing room to kite.
Icy Abyss Naiads are rough and can shut down groups if you're not careful. Their big ability to watch out for is when they have a bubble forming above them; they will launch projectiles that will deal damage and trap the hit player in a bubble--which can be chained to deadly results (often if multiple players are standing near each other).
If your group is having trouble with the Icy Abyss Naiads I strongly recommend simply targeting it first.
I like to pull the east group from the opposite side. This group is relatively easy.
For this last group I clear out all the spare kelps on the side of the map that's convenient depending on which vertical Kraken was cleared out. This pull is the same as the one before the 1st Gate, sans swarm-types. Like previous pulls there's plenty of room for kiting.
Gauntlet => Cetus
This section has another 3 groups of mobs along with an extra quirk: starting from the second turn (the path leading directly to Cetus), groups of kelps continually spawn from Cetus and march down that hall. If you pull smart, this is only really an issue for the last pull. Be aware that any kelps that spawn and reach the end of the hall will just sit there if not pulled and then slowly die, so you can wait for waves to despawn before moving forward.
The first pull is pretty easy, just one Foamy Tides Ong and some kelps. The thing to watch out for with Foamy Tide Ong is for when they start to spin around; they will start to do huge damage in melee range.
Second pull is an ong with 2 support kelps. I strongly recommend pulling these back around the corner to where the first group was to avoid having to deal with the spawning kelps.
Third pull is a bit trickier unless you pull them far back around the corner, then it's just mostly dealing with Icy Abyss Naiad shenanigans while you take down the ongs.
Before moving on to Cetus, I recommend waiting for a wave of kelps to pass and then blitz straight for the boss, picking up kelps along the way, instead of stopping to fight them, because if you do you will start to get bogged down by rapidly spawning waves as you approach.
Cetus himself is pretty benign, the real trouble is with the intermittently spawning kelps, which can do real damage if they're not managed.
A lot of my troubles tanking this fight have been solved by simply kiting full time and picking up adds as they spawn. It makes the fight very safe for everyone.
Leida the Conquerer
I recommend clearing out all the kelps in the courtyard leading up to Leida just to minimize the risk of extra accidental pulls during the boss.
Leida is a pretty simple fight. The first, most immediate thing to watch for is geysers that will spawn beneath players and then erupt, dealing large damage if they're not avoided. Second, at 15x and 7x HP, Leida will create a shield and spawn two Naiads. The shield reduces damage to the boss and deals damage to anyone standing inside it; to break it, both Naiads need to be killed.
The two Naiads spawn at opposite sides to the left and right, which can make them tricky to pick up. Often, one may wander into Leida's shield, in which case they need to be pulled out (with either abilities or manually--can retreat a bit into the courtyard). If you can get threat on both quickly, you can cause them to cluster up by moving into the recess on the right/west that you can see in the background of the above screenshot.
Elsewise she's pretty easy to shred down, putting an end to MSM.
