I'm starting to suck less with Mordekaiser (and in general.) Had a couple good AI games with Webadict/Realmfighter last night, so I hope I can either afford him by the time he rotates out or there's one I can not suck with next week.
I also want to try Malz before he's gone.
Mordekaiser is quite simple to play. When playing him, don't think you're a tank: Yes, you have your shield, but it doesn't make you into a good tank. Instead, get damage early on, that keeps your shield up better as well = also more tanky.
Regrowth pendant is a very good choice for first item, but don't build it into FoN the moment you get the cash. Instead, build stuff like MPen (Sorcerer's Boots, Haunting Guise) since all of Morde's abilities deal magic dmg, MPen helps very much to deal damage - and get your shield up.
After those items you can start getting tanky. Since Morde has zero CC, not even slows, Rylai's Scepter works really well for him. Also, Abyssal Scepter.
Spellvamp isn't bad on him either, 2 gunblades, some Mpen and no CC used on him = he is really hard to kill.
I consider myself a pro Morde (match history ftw), but I can say that there are some matchups you just can't win with him. If your enemy is a powerful, consistent and aggressive harasser you probably won't win the lane. If they hesitate at all, really, the lane's yours. Until you go back your first time to buy the appropriate defense item you won't have a very good time against people like Ez, Ashe, and Teemo. AP matchups are the best for Morde.
I usually have 2 regrowths, level 1 boots, chain armor ,negatron cloak, and amplifying tome by the middle/end of laning. Depending on what their team is and how we're doing, I build Mejais, Force of Nature, Randuins/Thornmail, and Sorc/Merc Boots in no particular order. Usually I start out with the mejais first to get stacks as early as possible. The mejais takes care of AP problems early on so you can focus on building defense while also dealing more damage. Rylais and a final situational item come after.
I shy away from anything with AD because with Morde your main asset is your AOE damage since you don't bring CC to the table, any ranged/melee carry takes care of the AD job better. And since you aren't Vlad I don't find a revolver worth it because I'd rather have damage/survivability than sustain. After FoN, you won't have HP problems anymore regardless, and you'll heal for an insignificant amount in teamfights.
tl;dr : Spam AOE damage while being extremely tanky, ghost their carry and use it to destroy them harder. While ghosting an AP carry gives you more AP, their auto-attacking Caitlyn will be of more use to your team than their auto-attacking 1000 AP Karthus.