How to use thunder storm?

Solution 1:

Casting shield + water + frost + lightning will give you a personal shield that will protect you from melee and lightning damage. Use that instead of a shield aura to prevent enemies piggybacking on your lightning immunity. Keep in mind that a single thunderbolt will strip you of this shield, and you will need to cast an aura of water immunity to protect yourself from getting shocked due to being wet while re-casting the spell.

There is no reliable way to make thunderstorm hit the enemies more often than it normally would. Thunderbolts will randomly strike within 25 yards of the caster's location, biased towards the 20 yard mark and will hit elevated points more often.

Alternatively, wear the Tron robe that gives you lightning absorbtion for full healing whenever you are struck by a lightning bolt. Warning: prolonged exposure to the Tron robe may cause cheesiness.

Solution 2:

Taken from this question

[QFAER] Water, Lightning | Prevents Wet (Very useful in Thunderstorm)

you might want to add additional lightning resistance [QFAAER] for increased durability