Leveling Illusion Fast Edit
This is one of the easiest skills to level, all you need is a calm spell. These can be purchased from most magical vendors. Find an NPC, preferably in a small room or one that doesn’t move much, I used someone sitting on a Throne. Keep casting it on the NPC, rest for one hour when it gets low and repeat over and over again. This is free, easy and a great way to increase your overall level. Another method of leveling Illusion is to get the Muffle spell, it is available to purchase in whiterun from the court wizard. Muffle(look below to see what Muffle is and where to get it) is a self-cast that only takes 2-3 casts per level while your Illusion skill is below 50, and can take you up to lvl 100. Can be cast repeatedly while out adventuring.
Buy or obtain and equip courage a novice level spell. equip it to both hands and cast it repeatedly on any npc it does no damage so they wont really care. It will take about 40 min to get to 100.