AP Nasus probably has one of the most annoying laning phases for the enemy to deal with. The two main attributes that makes a great AP Nasus is POSITIONING and MANA CONTROL.

POSITIONING: The reason why AP Nasus is so cheese is because you are actually unpunishable by most enemies when you Spirit Fire them. If you can get really good at Spirit Fire from a safe distance then you are already on your way to being a master wizard doggo. The more you play AP Nasus, the better you will get at Spirit Fire from max range. Remember that your Spirit Fire does more burn damage after the initial cast so ideally you would want to Spirit Fire the center of the enemy but sometimes it is better to Spirit Fire them from max range because it is safer.

MANA CONTROL: AP Nasus doesn't really come online until your first back so be very careful not to spam your Spirit Fire too much because you will become OOM very quickly. Generally I will Spirit Fire the enemy when my Arcane Comet and Manaflowband are up and then wait for them to come back up again before Spirit Fire. If they are low enough you can flash Spirit Fire (and ignite if you reach) to finish them.

PLEASE BE PATIENT: I am not kidding when I say that you suck until first back. Just make it a personal goal to first back for Blasting Wand/Sorc boots/Hextech Alt/Lost Chapter (Any of those and of course always Dark Seal if you can) and then you feel your wizard powers come online! However, don't get ahead of yourself apprentice wizard, you will still have to be patient. AP Nasus is definitely a different playstyle. YOU NEED TO PLAY LIKE A MOSQUITO. You have to slowly wither them for their health with your Spirit Fire until they are low! After they are low they will either 1) overstay in lane which allows you to oneshot them OR 2) they recall, which is also a win because they lose xp and gold.

NASUS LIKES GANKS: Nasus wither is AMAZING for ganks. As soon as you see your jungler come in walk up and hit them with the wither. You can also Wither people to stay in your Spirit Fire for longer since it does ticking damage.

DON'T UNDERESTIMATE YOUR ULT: Do not be afraid to use your Fury of the Sands to get out of sticky situations. (Or to win) You aren't building tank but you are still surprisingly tanky when you press Fury of the Sands. The burn damage is also very strong once you get some AP. I have won many fights by simply walking on them with my Fury of the Sands and the enemy not expecting that much damage. No one seems to remember that Nasus Fury of the Sands can do nasty damage.

DON'T FORGET ABOUT PASSIVE: Nasus is very good at healing up after a trade. Typically you want to not even allow them to trade you but sometimes it just happens. The doggo has to CS so you will take damage. Just don't forget that you will heal up a bunch after autoing/ Siphoning Strike minions.

DON'T FORGET YOUR STACKS: You are still playing Nasus so please stack accordingly. If you can get the stacks then your Siphoning Strike will still hurt very bad! A good AP Nasus will also be able to BONK you with his wizard stick. If you do prefer more the BONK playstyle then feel free to buy a Lich Bane!

BE AWARE OF DAMAGING THE MINION WAVE: A consequence to constantly poking with your Spirit Fire is that you will naturally push the wave. This isn't necessarily bad because you can still poke them while they CS under tower, BUT you need to have good vision and be very careful of ganks! If you don't want the wave to push as hard I advise placing your Spirit Fire so that they don't hit the minions (or at least not the whole wave) when you poke them. This can sometimes be very difficult. A trick that you can use against laners that respect your damage is to just walk towards them so they run away and you can Spirit Fire them behind the wave. Obviously this only works if they are scared of you so keep that in mind.

This is where you need to play very smart and calculated. Please do not just throw out your Spirit Fire. Try to place it where most of the enemies are standing! And hit as many as you can!

DO NOT ENGAGE: Unless they are caught out you typically don't want to engage. Wait until the fight starts and then place the massive E!

PRIORITIZE SQUISHIES: Trust me when I say it's better to Spirit Fire the backline than the engaging tank.

ABUSE YOUR AOE: Like I said earlier, unlike other wizard champs you actually have a huge aoe. It might not seem like you are contributing too much to the team but remember if you Spirit Fire correctly then multiple people will take all that damage. Try to get as many people in it as possible! You will be surprised at the damage charts!

Sadly AP Nasus isn't amazing into tanky/bruiser teamcomps. In this case you can go "Incinerator" Nasus but I'd still be careful. Also you will run into plenty of champions that you just can't do much against. Champs that have really good sustain and/or range are pretty tough to deal with. The point of AP Nasus is to slowly wither your laner down, so if they just heal it back then you are pretty useless. Also because your range is what you are abusing he tends to suck against longer ranged mages because they can basically do what you do but better.

Thank you for reading this guide. It is my first guide so please feel free the criticize. Sadly AP Nasus isn't so popular so I thought I'd give him some love. Lastly: PLAY AT YOUR OWN DISCRETION lol, sometimes it works, sometimes it doesn't.