Sejuani is a mashup of a tanky-jungler and a crowd-controlling, lane pusher. She can be built to lane and to jungle; I've tried both and I prefer her as a jungler. This guide is built around clearing the jungle quickly and setting yourself up for ganks often.

Clearing the Jungle

SPAM YOUR W! IT IS YOUR DAMAGE DEALER AND MOVES YOU THROUGH THE JUNGLE MORE QUICKLY!

Start at blue: you want the cooldown reduction and mana regeneration. You'll want to get first hit, but have someone supporting and applying damage. Once you use smite, you should be two hits from finishing the golem. Your leasher needs to leave immediately.

Continue to wolves, then the ghouls, then golems. This should put you around level 3 and ready to gank bottom if they are being pushy. Ideally, ping the DPS champion in bottom lane and use your Q to keep them in firing range. Don't get greedy, you're not tanky enough...

...if you can't gank and you're low health, recall and then move to red. Take the red buff, ghouls, wolves, and then gank your top. At this point you should be able to clear any portion of the jungle in a timely manner.

Ganking Order and Strategies

Typically, I gank Bottom, Top, Middle, Top and repeat. It is arguable that they will catch on to the pattern, but Sejuani can move rapidly through the jungle and therefore offers unusual gank timings.

When I do gank, I lead in with my Q to start it's cooldown and immediately use W to start dealing damage. I'll follow up with Exhaust if it is available so my team can apply more damage. If my ultimate is ready, I will use it ASAP. If it is not, E will slow them long enough to get my Q up again. Spamming Sejuani's abilties is important. I typically avoid taking the kill, as I prefer to feed the team members who are in lane.

Greater Mark of Resilience and Greater Seal of Resilience

You need to be able to survive the jungle and be able to take damage when you're ganking. These runes give you an edge over monsters and unprepared champions.

Greater Glyph of Focus

Without CDR, you'll find yourself wishing an ability was ready more often than you should. Being able to spam CC abilities more often helps not only when jungling, but during team fights as well.

Greater Quintessence of Strength

Your frost passive requires your basic attack and therefore, increasing the damage that attack does would makes sense. These Quints can also be replaced with Quints of Avarice (Gold) or Defense (Armor/lvl) based on your needs.

Offense

Summoner's Wrath: Makes your Exhaust ability more powerful, allowing your team to deal more damage while ganking.

Defense

Generally you want to increase your health, reduce incoming damage, return damage and increase your movement speed. This allows you to be more tanky and last longer in the jungle and during team fights. Taking Summoner's Resolve allows your smite to be more beneficial.

Utility

I take Summoner's Insight to make flash more useful if I decide to replace Exhaust with it. I'll use Flash in cases where the opposing team moves more quickly or if I plan to counter-jungle.

Other than that, take mana per level, movement speed, gold over time, and buff enhancements.

I prefer Smite and Exhaust. Smite because I'm jungling and Exhaust because it makes my ganks more successful. As stated in the Masteries section, I'll take Flash in cases where I need to counter-jungle or if the opposing team composition includes fast-moving or CC champions.

Passive: Frost

Sejuani's basic attacks apply frost, reducing enemy movement speed by 10% for 3 seconds.

Explanation:
Frost is great and makes ganking more successful. Pair this with Attack Damage runes to increase effectiveness of your hits.

Q: Arctic Assault

Sejuani charges forward, dealing 60 / 90 / 130 / 170 / 210 (+40% of ability power) magic damage and applying frost to enemies. Sejuani stops upon colliding with an enemy champion.

Range 700
Cooldown 19 / 17 / 15 / 13 / 11 seconds
Cost 70 / 80 / 90 / 100 / 110 mana

Explanation:
Take your Q second, maxing it second. It won't help you jungle, and you won't be ganking until level two. You're more concerned about the CC ability here and want to make sure your W is the damage-dealing ability.

W: Northern Winds

Sejuani summons an arctic storm around her for 5 seconds, dealing magic 12 / 18 / 24 / 30 / 36 +(10% of ability power) + ( 1 / 1.25 / 1.5 / 1.75 / 2% of maximum health) damage each second to nearby enemies.
Damage is increased by 50% against enemies affected by frost or Permafrost

Cost 40 mana
Cooldown 10 seconds

Explanation:
Take W and max it first. Using this constantly allows more damage to be dealt while jungling and while chasing down champions who are affected by your Frost passive.

E: Permafrost

Sejuani converts frost on nearby enemies to Permafrost, dealing 60 / 110 / 160 / 210 / 260 +(50% of ability power) as magic damage and increasing the movement speed reduction by 30 / 40 / 50 / 60 / 70 % for 3 seconds.

Cost 55 mana
Cooldown 11 seconds

Explanation:
Take this fourth and max it last. You shouldn't need it until your second gank (as you have Exhaust). It is most useful when popped before your W, as champions will take extra damage.

R: Glacial Prison

Sejuani throws her weapon, stunning the first enemy champion hit for 2 seconds and all other nearby enemies for 1 second. All affected targets take 150 / 250 / 350 +(80% of ability power) as magic damage and are affected by frost.

Cost 100 mana
Cooldown 150 / 130 / 110 seconds
Range 1150

Explanation:
The thing to remember with Sejuani's ultimate is that it takes some time to travel. It has an area of effect blast, but be sure to lead properly when ganking to maximize it's effectiveness.