This is something I am learning as well from a user called Grape and I tried it. It works pretty well and is pretty fun. Always go in and target ONE champ at a time, always squishy first. Because you will not be playing full tank you wont be as tough as Sejuani is usually so be careful on remembering that. Always pick em off as that will be your job for team fights to get the best out of your team. I am still learning this as well and if I see anything else that works great then I will add it. Please understand, thanks!