This is my first guide for IC, so enjoy and i hope it will help you out.

To me, Superman is strong on 3 positions:

-Mid: He can farm faster wich leads to an early "Up Up and away" available, this could lead on good ganks on bot and top lanes. beside of that generally mid is taken by squishy targets who can be eated in no time by your skill combo.
-Jungle: the map is new, for me the jungle is a good place to go for superman, but not for now.
-Top: For me is the best place for bruisers right now, you can make good use of your tankyness up here.

First of all i wanna talk about stolen powers.

Teleport: As it is right now, GD is a huge map so teleport is a must for map control, speak with your teammates and have at least 2 champs with teleport.

Invulnerability: Is pretty much the most useful stolen power for bruisers right now. Take the Doomsday one cause of the extra shield.

The only other good option is flash super speed for chasing needs.

Now, with the amplifiers, take:

MODS:

-Claw of Horus: Wayne Enterprises Mod (200 credits off T1)
-Soultaker Katana: Queen industries Mod (+10 maximum Stacks T3)
-Suit of Sorrows: Wayne Enterprises Mod (+40% Reflect T4)

As an optional you can get (see the tanky way):

-Crime bible: Queen Industries Mod (Gain stacks every 60 secs)
-Lobo's Chain: Wayne enterprise Mod (+75 Health T3)
-Entropy Aegis: Lex Corp Mod (+75 Health T3)

Augments:

You can choose different for Superman depending on how you will build it, choose between: Health, Lifesteal, Attack Damage, movement speed.


Items:

Your 3 core items will always be (for exceptions see below):

-Suit of sorrows: Pure tankyness, a great buff for your passive and the reflect effect+Mod is awesome.
-Claw of Horus: A combination of Armor, AD and lifesteal, everything that Supes needs, add a passive that works best on those though guys.
-Soultaker Katana: Lifesteal and AD. Those stack works great on mid/late game.

Out of those 3, wich are a must, you need to take a look at the oposite team.

"The Damage way":

Superman like every bruiser needs to be build in orther to have a good damage output, so you can consider 3 options, going the damage output way or the tanky way or a mix.

-Deathstroke's Claymore: Incredible Sinergy with Claw of Horus and Soultaker Katana, especially for tankier opponents.
-Lobo's Chain: More Attack Damage, a nice buff to your Health and a great passive for chasing.
-Sword of beowulf: Only take this one if the enemy team APC (Joker, GL, Etc) is destroying everything.

"The Critical Way":

If you take this way, your last 3 items will be the following. "Kryptonian Might" (Q) crits are brutal.

-Joe Chilli's Revolver: Great source of damage, and those Criticals will make noise on every teamfight.
-Zeiss Goggles: Only buy if you are following "the critical way", doing so use the active wisely.
-Velocity Implants: Only buy if you are following "the critical way", the speed buff is nice (move/atk).

"The Tanky Way":

This is a strong build for Superman, and it is more strong if you combine this itemization with choosen Amps and Mods focusing on health and defense. If you are going this way replace "Soultaker Katana" and "Claw of horus" from the core and take the following.

-Crime Bible: With the mode applied you will get a health boost in no time. Rush it first.
-Lobo's Chain: More Attack Damage, a nice buff to your Health and a great passive for chasing.
-Entropy Aegis: Health Buff and Will Buff, Power Armor and a great Passive for those annoying Powe Damage hits.
-Fragment of mogo: Health buff, Attack Armor and a great passive for close encounters and TF.
-Spear of Destiny: Power Armor, AD and a passive that is the Bread and Butter of this build.

"The Anti-Power Damage build"

If you are facing a team of 4 (or 3 feed) Power damage based champions, i recommend you replacing "suit of sorrow" from the core and taking this ones.

-Sword of Beowulf: Your Much Needed AD, a Power Defense Buff and an awesome passive.
-Entropy Aegis: Health Buff and Will Buff, Power Armor and a great Passive for those annoying Powe Damage hits.
-Ra's Al Ghul Robe: Power and Attack Armor, and one of the best passives in-game.
-Spear of Destiny: Power Armor, AD, his passive wont be as useful as in "The tanky Way" but is needed.


If you are not using any of the builds stated above, consider for your personal build the items named as the strongest for Kal-El

Well, not much more to say. 

As i see it, atm Superman is one of the strongest Heroes in game, and the best Bruiser you can choose. His kit even if is a little "awkard" in good hands is extremely strong and can distrupt enemy team tacticts as easy as he says "Up Up And away"

Hope my guide will help you to manage him.

Thanks for reading, if you guys have any doubt, question or critics, comment them below and i will try to answer them the best i can.

Cya around!