When Ganking you have to inform the people in that lane. Use pings and only gank if they are at least on your side of the lane. For example if i was gonna gank i would inform and ping the champion i want to gank. Next i would wait for my team mate to use CC on them (crowd control) then i would go behind them with my q and then use my w then use my e. Ganking with sejuani is very effective because all her moves and he basic attack have slows on them. Rember to gank when you have red to enchance your ganking ability.

You dont have to build exactly my build. Build against the emeny team. Always look at your death recap and if you see that you died to for example annie 3 times it would be a good investment to get a negatron cloak. remeber 2 major items you would need though is a frozen mallet and warmog it also helps buff up your w.