At the beginning we have some problems on the lane. For high damage we need autoattacks, which are rather difficult to apply due to the limited range compared to other midlaners. Here it's all farm, farm, farm.

Once we have shoes and nashors tooth, we can start fighting. The first powerspike is enough to win a 1v1 against most champs without any problems. Feel free to try it out here.Depending on the enemy champ you can even start with the ult to apply the CC, possibly the burst damage is not enough. Here it is still dangerous. Remember to stack your W before using E and Q. The deflection time reduction is important for survival.

The second phase starts as soon as you have your mystical item. The true damage makes every champion a potential target. The burst damage is high and a 1v1 is hard to lose with a little experience. From Rabbadons on you are a true 1v1 monster and the ult can be applied to any target. Usually a R + W + Q combo is enough to kill targets. Exceptions are possibly toplane tanks that have MR stacked.

The last thing you do is get your tank items. Here it is important that you react situationally. Standard build is Gagoyles Stoneplate and Spirit Visage. If there are no AP champions in the opponent team, then Randuins or Steraks Gage with extremely high burst and CC.

MR Pen is not necessary. Riftmaker with his 9% True dmg alone ensures that your damage even with stacked MR is so high that it hardly matters. I tried for a long time with Full AP, but you are just a running target without escape possibilities. The two tankitems are much stronger than other AP items. As an example:
Even with only 3 AP items, as described above, an R + W + Q combination is enough to kill any AD / AP carry almost certainly over a long range.