Hi! I'm making this guide with confidence and pleasure tho Sejuani is only jungler that I can say I am pro with . If you follow my instructions, you will have good results ( I hope xD )

AP with a lot of Armor and some MR.

Your choice, but I recommend you 0/30/0 .

Start with W , then take E , you will give priority to E because it can deal damage from far and it will improve slow amount.
Do a lot of counterjungling, ward their blue and red.
When you are ganking, first you will turn on W, charge with Q ( try to hit Q because it will knock enemy in air ) , and target will have debuff, allowing you to activate your E. If he is not dead yet and he have chance to escape, make sure he won't , ULTI HIM! :D

Use W+E combo to make your farming easier. That's all, good luck in jungle!