First of all don't play against champs with ranged basic attacks
(You tend to run away when basic attacked so the ranged people will keep you from farming)

Laning early untill catalyst:

Do not engage the enemy.

Let them engage you.

Minions are #1 priority at all times.

Scenario:

You are happily farming AND OMG HE IS COMING AFTER YOU!

+ +
BANG you just slapped him silly and walk away.
Sometimes this ownage just weighs you down.

Don't be gulping down that potion everytime you do this!
It's a nice idea to do it the first time to shower him with fear and disgust!

Now you have most of your HP, took some of his, got a extra 10g in your pocket and looked hella sexy doing it!.
NOW GET BACK TO FARMING!

Enemy being mean?

YOU ARE A 2 METER HIGH FULLY ARMORED TANK WITH A ANCHOR!
USE THAT E, SLAP HIM WITH THAT ANCHOR, SCREAM AT HIM!

Or ask your jungler for help and try to keep minions on your side of the lane but ssshhh

After Catalyst:

Oh baby, it's the start of something lovely.
Together with your Corruption potion yo booty gonna stay in that lane.

Damage Check Time

Now let's see what color he poops
You see a nice chance? TAKE IT!:
+ + +
And casually swim away.

Now check the following:

Is your enemy crying over lost health while you are still swimming in mana?

Did your enemy sacrifice more to the blood gods then you did?

Was the enemy blinded with rage when you engaged?

If any of the first 2 are a no -> Time to scrub back to safe farming.
Enemy went crazy and went after you like a wild animal?:
Did you receive more damage then you could dish out? -> Time to scrub back to safe farming.

Wait whut? You won the fight?! GUESS WHO OWNS THIS LANE NOW!

Just came back from base? CHECK THAT FACE AGAIN!

Got them boots AND winning that lane?! Sweet! Take them rekking skills to mid a few times.

About the ult

You leave that bad boy for badass kills, escapes or sweet engages.

First off:
YOU are the nautilus. SCOURGE OF THE SEAS! WHO'S LANE IS THIS?!
THAT'S RIGHT IT'S YOURS!

Leave engaging off to lvl 3 when you have your full abilities (except for ult)

Remember:
You are not meant to be passively waiting.
You are a tanky beast with a giant anchor.
Time to put that baby to use.

Walk around a bit and use thatTo keep the money flowing as well.
You see a chance? TAKE IT!

+ + + +
Now if your adc isn't super slow he probably helped out and you kicked that booty to the back of the lane! Maybe even got a kill out of it together/

Heal up and try to stay in that lane untill you get enough for your first back.
Meanwhile try another engage while you are at it.

First/Second back

What is this?! TANKIER?! MORE ENGAGES! UUUAAAGH!!

By now you are level 6 wich means let's add a skill to your combo!
+ + + + +
BUT HOLD THE **** UP!
If they have a

MORGANA

It's time for a different approach!

First engage (probably the adc) withNow the shocked Morgana will probably stress shield her buddy so it's time to her to oblivion!

Rightous Glory

The moment you getis the moment your engages will be easier and you can start doing serious roaming stuff.

Just activate Rightous Glory and rush into them!
Unless you are 10000% sure they don't have there is no need to use .
When you get close you either hit them with your or they flash and you .

REEL THEM IN BABY!

The ult

Only for:

Kills (ADC can't reach? Yoink!)

Engages (Nothing is a better target then a flying fish)

Escapes (You can't catch what isn't in the same area)

Teamfights (5 flying fish in the air with a Rightous Glory after?! Change mah pants!)