Morgana is, in my opinion one of the best supports in the game. However I see so many Morgana players getting completely stomped out. Why? They build too much AP. If you buy AP in the first three items, then you're doing it wrong. Not only does she have a snare but her ulti is a double slow/stun. Morg is about her utility, not her damage, so make sure you have a team around you that can do so.

I personally don't like to return to base unless not doing so would leave me at a significant disadvantage (i.e. your enemy has lvl 2 boots and you still have none). Because of this I run a lot of mana regen. While this doesn't help at all really at late game, it is essential to the laning phase. Magic pen is also a must because of the lack of any substantial amount of AP.

There are two different masteries setups that I like to run. The one displayed (0/17/13) is the one i prefer to run when my team is a little squishy. The basic 9/0/21 (extra magic pen in offense, and maximizing mana regen in utility) is what I typically use for 9 out of 10 games.

I start by taking a regrowth pendant and depending on how confident you feel, a mana pot or a health pot. When you reach 1565 gold or more and you could use a break, go back and pick up a philosophers stone and Merc Treads. The extra movespeed early will make hitting your snare so much easier.

Morg is a support with relatively high cooldowns. Now that just cant happen. Rush a Glacial Shroud and that should be just about all the CDR you need.

Rylais should be next (take the AP items first) The one ability with no cc is morgana's pool. Once it has a slow you might as well /all "just try and run away"

This should be the point where you wipe the enemy team, walk down mid and blow up that big thing with the big crystal on it. If not, finish the frozen heart.

Abyssal and WotA should make anybody else with AP on your team hit like a truck.

If you still haven't won then pick up a hat and start landing the snare.

Get one point of snare at level one and leave it there. Max the AoE first, then the shield, scaling the ulti whenever possible. The W is what gives Morg some creep pushing power and damage dealing capability. Her shield is also one of the most annoying things in the world for enemy teams with any cc at all.

There are a few rules that make playing morg easy

1. Stay close enough to your carry to put the shield on them when they need it

2. When their creeps stop moving put down a pool that will hit as many of them as possible

3. Use you're ulti any time its up and there's 2 or more enemies nearby.

4. Hit your snare

Its hard to find an argument not to take flash. The other spell is really more up to you. I like fortify, nothing quite says "screw you" like a fortify for that annoying bd. If you decide to go 9/0/21 taking the upgraded clairvoyance is always nice for that pesky bushdweller. Teleport is also another good one. Summoner spells are really up to you. Play her a few times and figure out what you like.

I'm not going to tell you what to do because there is no way I can account for the human variable. However i will tell you when it's a good idea to pick Morg.

-There is a Lux or Karthus on the enemy team (you're shield is an *** saver for both of their ultimates)
-There is 2 or more hard cc's on the enemy team (Stun, Fear, Snare)
-Your team lacks pushing power.

One technique i have found works is what I call the "wall of minions"
If the enemy is down to their inhibitor turrets and is defending well use this

Starting at either top or bot put a pool down and push the minions to enemy turret. As soon as they begin attacking the turret go to mid and do the same. Then go to the last lane and repeat again. Go back to mid, push minions. I typically get to mid twice before my team figures out what to do and begins to help. I have also repeated the whole cycle 5+ times and single-handedly pushed down turrets. Its hard to say how the enemy will react. Some will recognize what you are doing and run out to try and kill you. 90% of the time however, your 4 teamates seem like a much better target to go after, because really, how much damage could Morg do ;)