Introduction
Once again this guide needs a complete overhaul with the changes to Shazam from Bruiser to Enforcer. As an initial warning Shazam is kinda weak compared to other enforcers, so if you still are keen on playing Shazam, let's try to make your experience as bearable or even enjoyable as posible.




Skills
The most important part about Shazam right now is to understand his pasive, Power of Zeus. Each 4th skill you use will be empowered and will have an aditional utility. Also gives you balls of lightning in your hands to show that the next skill will be empowered.

Your Q, Mystic power, throws a tiny lightning ball that will bounce to nearby targets after it hits, If empowered the first target hit will become stunned. (DRAMATIZATION, IT MAY LOOK LESS IMPRESIVE OR DAMAGING INGAME)

Your W, Mystic defense, surrounds Shazam in a protective shield that increases his armor and power armor for 2 seconds. If empowered the amount of armors given are doubled.

Your E, Lightning field gives you exactly what it says, a circle of lightning around you that damages enemies into it. If empowered this skills slows the enemies in the field.

Finally R, Shazam! makes you jump to the targeted location where you unleash a big lightning that will silence all hit targets for 1sec and damage them. This skill does not have a empowered version but it count as an skill used for the pasive and will not consume it, so your don't have to worry about wasting empowerment in a skill that won't give you anything aditional.

Now to the leveling explanation!
Your 1st level skill should be Q or E and it's entirely your choice depending if you want that early range poke or aoe damage, you should wait to see who you are facing before decide. If you are solo lane and get a double lane with pokes or ranged people Q may be more useful to last hit from safety. On the other hand a heavy autohit enemy you are better with E first as you can kill drones easily with it while getting free damage to him and he will risk getting drone agro attacking you.

Anyway no matter what you choose, your 1st skill to max should be E as it's your most non ultimate damage skill. After it level your pasive, as your utility is tied to the rank of it you should aim to get it maxed quickly too, 70% slow at max rank with empowered E is huge! And of course level you ultimate always when you are allowed to.

And now we get to a controversial point, maxing Q vs maxing W. You will probably have noticed I didn't say anywhere to put a point in W, the reason being that you shouldn't. Why you may ask? Because it has a whooping 60 energy cost at rank 1, thats more than half your pool for a 2 sec buff, and I think it's better to invest into maxing E damage or your utility than that. But when that is done, you are left with a choice, maxing Q to get a little more of damage or putting points in W to reduce the cost to 30 at max, which is more bearable. I think this really boils down to how your teamfights will be. If your enemy comp has a lot of movement skills (Atomic Wonder Woman for example) they will try to ignore you and go for your carries. In this case it would be more useful to dish as much damage as posible than getting defensive as the enemy won't attack you much anyway. 
In the end this is one of the things were personal experience comes in, once you get E and pasive maxed, the rest is your choice, as you have you core utility already.

 
Amplifiers, stolen powers and items
For amplifiers, Health and Armors are king for you, as HP also gives you more damage to your E while letting you survive more coupled with armor. Movespeed is also nice as Shazam is very one of the slowest enforcers.

Best Mods to get are debatable, but the best I have found for me are empowered Atlantean Seal, as having a slow when using non empowered E makes us less dependant on the pasive, followed by Enhanced health for Fragment of Mogo and empowered suit of sorrow as reflect damage is very strong atm. You can also consider Enhanced Nil Cloak if you have problems last hitting drones and empowered marauder ring if you are jungling.

Stolen powers depends of your team and role:
If you are jungling, Consume and Detonate are the best for speed clearing, but you can run teleport instead if your team is good setting cameras to get a good positioning at gank or Psychic Assault for extra slow.
If you are laning, cameras are a must as vision the most important "stat" in the game. The second one is once again your choince, Barrier is good to give you an edge in close trades, Teleport for surprise ganks in other lanes, and Super strenght is good because throwing meteors and cars to the enemies is cool. Psychic Assault to help your jungle ganks is useful too.

For items, go marauder ring and shield for max damage and survivality in jungle, and go Nil Cloak/Weapon for laning. In both case buy 3 hp potions too. I ignored Nil Ring because in lane it doesn't help you survive more, but cloak with hp reg and weapon with the pasive will.
After that, you get a choice, go Fragment of Mogo for extra damage at max tier and survivality or Atlantean Royal Seal for more utility and constant damage. After those 2 go for Suit of sorrows or Mirror master prism depending of your enemy comp. As a rule of thumb get hp tanky items to counter the enemy main damage dealers and/or get more damage with Cosmic Staff or Book Eternity if you ahead in credits and feel more confortable with it.
As conclusion to this part I want to tell you that as each player is diferent, your item choice can be diferent too. This is what works for me, but it may not fit your playstyle so think of this as a stepping stone to the build you will be confortable with.

 
Gameplay
General

In case you haven't noticed yet, you are a tank and as the tank you have 2 main things to do. Initiate teamfights and protect your teammates, mainly your carries. For the first you notice that engaging with Ultimate followed by empowered E is very strong and will force the enemy team to engage or use their escape skills if they have them to move away. Be careful with your energy management as you don't want to be empty in a critical moment, but at the same time you need to have empowerement up as much as posible. For that the best way is to spam E to gain charges as it's the most efficient considering energy spent and CD. 

This general explanation covers more of what you are going to do mid and late game and  explaining them again is going to be redunfant, so let's go for the early game explanation!

Early

If you are jungling there is nothing special I can teach you that wouldn't be covered in one of the excellent general jungle guides this site has so go read one of them for that, it will also be useful to know how enemy junglers will behave.
If you are laning, you are going to have a hard time if the enemy has some kind of ranged ability to poke you, so try to last hit as much as you can, let him push the lane to get the chance for a gank, and use E in case you are overwhelmed with enemy drones or against the tower for fast clearing and a lots of last hits. As soon as you are lv 6 there is no excuse for your jungler to not gank your lane as you will be able to join the gank inmediatly with the ultimate awesome range and the empowered E huge slow will keep him in place enough time to blast him.

I think this covers all you need to know to be a succesful Shazam, or at least to begin to be one but if you want to know more, feel free to comment and ask so i can add it to this guide.