-Dont get involved in too many short trades,since your champ profits from longer fights because of his passive
-Wait for sidesteps before you use your Q ability.Be patient!
-Try to stay safe pre 6 and focus more on wave management than on trading the opponent (No Qs on minions just to deal a bit of dmg to the enemy)
-Think carefully who you should be ulting in teamfights.You shoudlnt just ult whomever you can kill in a 1v1 situation but who causes the most disruption in your team during a fight.
-Mordekaiser is a extremely versatile champ and you should try to make use of it.You can play him as a sidelaner or not, build him like a tank or an AP carry depending on what your team needs.
-You need to be patient regardless of how fed you became during laning phase. The enemy backline will have a lot of respect and try not to get ulted by you, so usually its better to hold your ult for a while instead of flashing into the enemy backline and ult their carry straight away.Set up a fight yourself so the enemy has to come to you!
-No matter if you bought some items that will help you in sidelane or not Mordekaiser is very useful in the sidelane and this advantage should be used from time to time. Remember that your ult turns any 2v1,3v1,4v1 or 5v1 into a 1v1 so ganking you is really hard and a lot of people will avoid ganking you because of it.