hi , i started playing sejuani at first day and i found these things that might help u:
1) I know it's not appreciated but if u wait to use permafrost until enemy is low lvl u can easely get alot of kills , even as tank

2) you should build her like i say in this guide , you need wrigles for early armor , wards and faster jungle , then u o wargmog and impaler so u are very tanky and still do nice dmg.

3) try not to waiste your ult : so initiate a fight whit the dash , permafrost , winds
when you hole team jumped in , u can use your ult to stunn evry1 on team , best followed whit a kennen ult or sona ult , so u'll win teamfights , speak whit your team to say in what order they should use their ults.

as u see , i take permafrost at lvl4, some people like to get nothern winds to skill lvl 3 first and then keep it there , but i found that if you got blue it jungles much faster if you doe permafrost 1 level higher.
the charge is leveld as last , because i only use it to put my passive on a group of minions or to dash thro walls

sejuani is kinda hard to jungle early game, so you best practice whit a couple of champs before jungle sejuani .
i like to start at blue , becasue u really need blue buff to jungle sejuani , good tip to counter her : if you steal blue she can't do annyhting.
Let some1 pull blue and do some damage , becaus sejuani doesn't have lot dmg at low lvl,
then u go wolfs-> raves-> golems (use smite here again) now go back to buy sword or boots , now go to red (smite woold be up again) , then i do this untill lvl 6 , then start ganking.
ganking is important , but u better farm alot so u get warmog and impaler , then u own lategame

for summoner spells:
1) smite: for 10g per time and you jungle -.-
2) flash: because she is verry slow and u don't really need exhaust
exhaust slows enemys for 40% , permafrost slows for 50%

i've seen that manny builds use the gold per 10 .
but i found if u start wriggles the jungle goes much faster and you get kills easyer:
so at the end u get more money using wriggles then golden haert and the pendant.
after wriggles i buy treads becaus it gives magic resist (MR) and then i have armor and MR early game.
then i go for warmog , becasu winds give a damage based on health and early game u don't need more armor or MR or damage .
after warmog i go impaler , then u should have around 200 AD and u'r a dangerous tank that can 2vs1.
now i buy angels becaus when i start the fight evry1 will focus me , and if i die my team will finish them off before i revive.
for the 6th item u can choose what u want , i usually go another warmog for 5K health and 250AD but u can also buy thornmail or nature for armor or MR
i also tryd lich bane as 6th item , but it didn't work out well for me =/

pro: strong lategame tank/dmg, strong ganks at lvl 6+, a stronger ult stun then sona

contra: hard to jungle low lvl , when they steal ur blue it's verry hard to jungle,
slow movement speed

if you play sejuani like in this guide as a tank:
you should speak whit your team to say when u use ur ult and when they use theirs, it would be useless to use your ult at smae time as sona ult.
normally u have to start the fights , but their are exeptions;
EG. when you have a veigar , let him stunn the team and then u jump in.
If you have a champion who has a stun on his normal abilitys (not ulti) yuo should let him do that first , then tank jumps in and u should win the fights.
Never run away from teamfights , then they easely pick u off while running.