Laning- The laning phase is pretty simple, just bonk the enemy with Qs and try to farm well. Morde excels in extended trades with both Conq and Lethal Tempo, and his W shield lets him come out of most trades ahead. He powerspikes at level 6 due to his ultimate allowing him to win most 1v1s and even 1v2s if you hit isolated Qs or hit both enemies with it. Leeching Leer is also a big buy because of the small but useful healing it gives, as well as a good hunk of health and some Ap.

Mid game- In the mid game you should be moving around the map to get kills, dragons, and towers. Split pushing is good if not much is happening or if your other lanes are winning. By this point you can effectively 1v2 just about anyone if they aren't fed. You aren't too tanky at this point so you might get blown up in team fights if you are focused, but can deal lots of damage if you aren't.

Late game- By this point you are a near unkillable teamfighting god. You'll have big aoe damage, a way to neutralize any threats with ult, big heals and BIG shields. Theres not much to say about the late game, you're just a near unstoppable wall of death and metal.

Things that screw you over- Quicksilver Sash, Gangplank W, and Olaf R are a few of the things that can cancel your ult. A very important piece of knowledge is that Qss does NOT remove the -10% stats debut, so you can still fight enemies, but they can escape.

A few tips- Always ult the enemy jungler at dragon fights so they can't Smite it
E can be used to pull people behind you
You can press Q then flash to get a long range Q
Don't use you W recast in combat as the heal will always be less than what the shield currently is

1v1 vs melee- 1v1ing against melee is simple as Mordekaiser. Just press R and right click, with the occasional Qs thrown in there. Speaking of Qs, hitting them is absolutely necessary. If you miss them against other good duelists like Darius or Irelia you're screwed but if you do hit them you have a god chance of winning.

1v1 vs ranged- NEVER ult a ranged champion without hitting your E first. that is one of the dumbest things you can do as Morde. You waste so much time trying to get onto them in your ult if you don't hit E and you just spend the duration trying to get onto them. If you manage to hit them with something that process Rylais or Cosmic Drive you can ult because of the bonus move speed/slow letting you get onto them quickly enough. Try not to Q when the ranged champion is outside of your passive range as it will let them escape since you can't move as you cast it.

Team fighting- Morde is one of the best team fighting top laners at the moment. His massive aoe damage, big shields and considerable amounts of healing, and a way to lock down the enemy carry make him an absurd team fighter. What you want to do is get your passive up and ult either the enemy mage or ADC. Ulting the enemy mage is usually the better option since you will get 10% of their Ap. Ult the enemy ADC if they pose too much of a threat to your team and need to be eliminated, or if they need to be out of a fight for some time. after take out one of them, move on and shred the enemy team with the stolen stats. Do not wait until you are at low health to use W. Always use it whenever it is full so you don't end up dying after using it; you have a good chunk of health instead.