I have noticed that people think after 2 times being in 4-man dungeon they are more than qualified to join in anytime. Maybe it might be so for some but most of the time people need way more experience until they can finally be able to do the dungeons with few mistakes allowed.
One thing that has appeared more clear than others is that too many people rely on FM or the Dragonblood in 6-mans to survive through certain points. Also there is no “random freeze” in yeti (people should see the spakles). In 6-man there is the indicator when to use skill to avoid getting frozen and this is making it much harder for people to learn for 4-man. Instead of focusing on what boss does they simply click on right time when the indicator tells.
So here is the one easy tip how to practice for 4-mans in 6-man dungeon. Make sure you have the option shown in picture unchecked. That makes it so that you cannot see the spacebar indicator and instead you have to learn the mechanism and animations.
This was made as a must in my clan and I must say at first it was hard but eventually I learned to focus on the boss animations instead of relying on indicators that tells to dodge upcoming boss skill.