A casual group is, well, casual groups don't tend to write kin policies like that. Generally, such groups still have as their goal the gradual clearing of content. They might not be able to clear everything, and almost certainly not on T2/CM, but without perceptible progression, even "casuals" will grow disillusioned.
It is a good idea to start with below level-cap raids. Turtle, Watcher, BG, OD, Draigoch, Orthanc. In that order. This is to minimize frustration due to players being undergeared, underskilled, or uncoordinated.
(2) Raid leader(s).
These people must have a good understanding of the mechanics of the raid(s) being run, whether from research or experience. They also need to know the key class skills, such as captain's In Harms Way/Last Stand, minstrel's Call to Greatness, and LM's Call to the Valar reset. Raid leaders are responsible for assigning roles to raid attendants based on the particular class/player combination present at any given raid. These roles are unlikely to be the same as in the posted strategies/videos/previous runs. Hence knowledge of multiple classes.
Most raids in-game (lair raids: Turtle, Watcher, and Draigoch excluded) want the following classes:
1 or 2 burgs
3 or 4 other dps, perferably a mix of ranged and melee
I do not know of a raid that needs 3 tanks. There are several single-tank fights. There are very few fights that favor 3 healers (Ivar and Durin's Bane in OD, Saruman in Orthanc, on T2), and even fewer that go faster with 1 healer (Acid in Orthanc, T2, zerg method).
Therefore, keep an eye on what classes your current group has and recruit/gear alts accordingly.
Failure in under-levelled raids is likely a result of a misunderstanding of fight mechanics or lack of coordination, and usually both. Therefore, practicing on these fights can be helpful in teaching the group how to play with one another and how to follow instructions.
Some members of the group might, unfortunately, be lacking in these respects. Make sure to help them improve. A group does not progress easily when such faults go unnoticed.
For at-level raids, progression might be furthur checked by player skill. A group in which the highest dpsers do 1k dps is not going to have much luck in T2 Orthanc. In such cases, the leader might want to decide whether to continue attempting the fight. That said, T1 Orthanc as well as Draigoch impose virtually no skill requirement on the players, only the ability to follow instructions.
(5) Learning as a group.
The raid leader should have a plan for the group before starting a fight. However, this plan is unlikely to go perfectly. (Actually, it hardly ever does.) Moreover, things will go wrong. CCs break. Tanking failures. DPS target confusion. Not enough heals. Etc. In such cases, a good group might be able to recover. Re-CC. Emergency offtank. Switching targets. Use cooldowns. And then, if a wipe nevertheless occurs, the group is able to see what went wrong and how to prevent it from happening again, or how to react better next time.
I'd like to call this raid-wide situational awareness. It happens when people know how each other is going to react in various situations. It is the reason why certain groups seem to clear content faster/more efficiently/in fewer attempts than others.
-- From a former Imladris raid leader, currently on Elendilmir.
Tityla said it perfectly. One thing I would add is to have a core group when doing tougher raids. (ToO t2, maybe saruman T1 if you havent done it yet.) After you have that core group, you can start swapping out players. Swap captain A for captain B, champ A for champ B etc. In the end, you have 9 people who know the fight and 3 that do not. 3 people should not cause a wipe unless its a major roll like a tank or captain with a specific job.