[Kristoffer O]

Use the Starspawn priest (150 g) or the Hero Cthugul. They are less likely (especially the hero) to get fried. They are not better at succeding, but with time and no insanity their skills will grow and they will be able to summon some rather powerful beings.

There is an increasing chance everey turn of a summoning (you do not get a monster every turn, but after 4 turns IIRC you have one for certain). Every successful summoning gives the summoner some experience in the summoning skill. When summoning increases the effects are better.