Nasus is a decent Off tank and late game Main Tank. However his strengths rely on his Q ability. His racial of 20% life steal means as long as your not running in staff swinging with no support behind you your going to maintain a lane.

Game start you will be place the skill point in your Q. This Attack will not only hit for massive damage but if it used to last hit minions/Champ/Jungle mobs its over attack will increase. Another added benefit is when you hit with your Q you are given more health back. Meaning that late game Q will decimate any and all challengers.

During level 2 place it in E. Usually you would use this skill point for W but your will not be doing much champ encounters early game to opt for you E. Your E is a crowd control area over effect. It is great for pushing champs away and getting easier minion last hits with your Q.

During level 3 place a skill point to your W. Your W is a slow. Plain and simple.

During the Crucial levels when you can level your Ultimate. DO IT! Your ult gives you health, the sands surrounding you damages all enemies around you and your Q hits for almost double of what it normally does in normal stance.

After this priority is Q, W, and E. Your slow will benefit you late game because cool down drops and the time slowed increases. E can definitely help with CC of getting a quick champ kill if you cant reach for the last hit.

Remember to always... ALWAYS farm Q. ALWAYS! Q = Win!