Your gameplay revolves around your W. If you play your W correctly, you will never lose a trade to anyone except a swain or a well played renekton.
Max W every game, no exception. It only fully works when cast on an ally nearby so know that your strength is tied to 1) the lane and 2) a teammate with CC or a hook.
Magic Pen is extremely valuable because when built AP (instead of bruiser), your ult will deal around 50% max health damage.
Take all the CS. Shove your lane and take a jungle camp, vision permitting.
Challenger morde mains take teleport. That works because they make better, more organized plays. Laymen like us should take Ignite or exhaust. Morde is pretty useless in a lot of ways so the only thing you need to do is create pressure by winning trades, oppressing the enemy laner, and taking objectives. Win lane, snowball into rift, once you leave lane ult dragon, use the dragon to take baron etc.
Lastly, go hard in the paint. Avoid building defensively. For example, don't build defensively in lane vs that riven. Build damage to kill her before she kills you. If you get ganked hard in the top lane without vision, do not try to run as you likely won't get away. Hug your minions with W in a 2v1 and focus down the squisher opponent to try and get an ult ghost. Unless they're higher elo players, they won't think to kite you; they'll just try to fight you and you can come out on top.
I take either a standard AP bruiser rune page or max magic pen vs tanks.
Death fire touch for attrition lanes, storm raiders for all-in lanes.
Item pool:
Liandry
Rylai
Void staff
Sorcery boots/tabbi/mercury
Spirit visage
Steraks gage
Guardian angel
Dead mans plate
Randuins omen
Trinity force
Rabadons
Ludens echo
The first 4 I listed are typically core for me