This guide is oriented to those who found funny as hell throw sappling to enemy and c them run, or go away from tower to avoid getting owned :)
First to said is that you can go mid lane and have fun there, but should be hard to get the kills you need to waste money, so try to get a lane, and if it's avaliable, with another one so you get in a 2v2 or 2v1 lane, and can completely disable an enemy.
Try to get a lane partner with some easy dmg, with no problems to do it, like a ranged, or a mage.I love teemo to get kills, and mage gragas is amazing to disable an enemy lane.

PRO:
Insane dmg from long distance + bound so not many ppl can run away from u when u wana harrass them
NOONE can safely go home at tower hahaha
CONS:
U'r so weak, even with ultimate up, u wont last so long, that's the point 4 RoA + Rylai

Basically i'm using a standar mage runes, so u can choose any other option, but dun forget you'r going as a mage, so AP/MP/CDR r most wanted here.
As I told b4 mage's masteries too, the ones u like more.I'm picking this coz your sappling is a mp leecher, so take care of the mp/tick coz u wanna throw them all the time

Maokai is mp dependant normaly so even more if u go to a complete AP set, so i think clarity is like a must.
On second, we got some choices:
ATT: as i dun think maokai needs more damage like ignite and of course neither like rally, i recomend to discard an attacking spell as the second one.
DEF: As we remember perfecly, we are squishy as hell, early on, so defensive skill will be our choice.
Ghost - Maokai is sooooooo slow and upgraded ghost may be a perfect choice, as we may need it to anything like last hit an enemy, or running like hell to defend a tower, but basically we wll use ghost to run away from the enemy players, any of them can hurt us a lot.

The skills u'r looking for is ur E, the sappling throw, coz is a 100%AP modifier+ 2 added damages. When u hit on throw+explosion u'll get the 100% of your AP in bonus dmg and the propper skill dmg, so it ROX!
Once this beind said, keep raising your sapling as much u can and get the root skill as your friendly dd, coz the ap bopnus it's so nice too.
I pick 1 arcane smash on lvl 4 coz being able to finish that stupid minions that moved away from the sapling, and also to combine with ultimate+root while sapling blows up in the enemy's face.
Your skill sequence to try an scare kill should b a sapling, activate the ulti,just as dmg, and while u cant xplode the ulti, root inside the ulti, and knockback with arcane, by that point sapling should b done, so xpolode ulti, and enjoy the kill. E/R/W/Q/R = Game Over

All the time u have no enemys on sight, your sappling throwed on the exactly spot, should b more than enough to kill the fully minions set, so keep going for that, and dun forget to always check bushes with your lil friend.
Getting tons of minions it's easy to get yourself geared up.