Sejuani is a melee, tank champion that is great to use. I use it because no many people use this champion, is a good tank and ganker, and I love frost champs.

As you use Sejuani you should know how to gank and how to use well her abilities so here we go !!

For starting we should get to know Sejuani´s abilities:

Frost: Is Sejuani passive, what it makes is slow the enemy by a 10% once Sejuani hit him/her for 3 seconds.

Arctic Assault is her Q ability. It makes Sejuani rush toward target location freezing enemies. If in the way there is an enemy champ Sejuani stops and freezes all champs

Northern Winds is the W ability. Creates cristalic winds which aply permafrost and damage to nearby enemies. If the enemy is forzen of permafrozen it strikes with 50% more damage.

Permafrost is the E ability. All nearby enemies affected by frost get Permafrost which slows the enemies causing them damage and slowing them for 30% to 70% depending level.

Glacial Prison: is one of the best ultimates (R key). Sejuani throws her weapon freezing the first enmy champion in the way stunning him and nearby enmies also but for shorter durarion.

Sequence:

For Sejuani there are 4 good summoner spells that i recommend:

Exhaust: is a great summoner spell to slow champions when they use things as [ghost] or are champions with great movement suh as Master Yi.

Ignite: Works very well for killing enemies in the case they run away with a liitle health.

Smite: As a ganker Sejuani would use Smite for killing the creatures at the forest though goin into the forests is ideal for junglers.

Flash: Is also recommended sometimes I change it for Exhaust though it works very well for catching enmemies or escaping.

This are very simple, for Sejuani I use 1/21/8 which is really helpful. I used Most Defense and utility as a tank.

For the runes is very simple is like the defense part so:

It has high armor, and magic resists. Also thereis +3.0 gol per 10 seconds, it is not much helpful but it works.

As a tank Sejuani is very basic to equip

I start the game with Boots and 3 Health Potion for then taking Mercury's Treads
>>
Then I get Kindlegem to make Shurelya's Battlesong

Next take Giant's Belt for Warmog's Armor

And finally I choose between Aegis of the Legion, Banshee's Veil, Guardian Angel, Frozen Heart, Frozen Mallet, or/and Sunfire Aegis.

As you gank with Sejuani you shoul go to forest first to raise level or got to bottom or top lane to level up fast.

In ganking I use this combo: I activate Northern Winds then i go and use Arctic Assault and then activate Permafrost for the enemy not to escape in somecases before the Northern Winds use Glacial Prison getting most of the times an easy kill or assist.

Finally here is a guide for you to get used to Sejuani and for winning with her.

Success for you and thanks.