Need hints & advices concerning summoning...

[Agema]

First ask, "Why Summon?"

You can summon units for a specific purpose. That might be just bulking out an army, getting new mages, or some specific tactical use.

Nearly all paths can get you bulk units, especially I think Death and Nature. The big exceptions are Fire and Astral, but they do have some neat summons in there. Air can bulk out an army, but not with much that can fight well, although it gives tactical options with flying units.

All magic paths can summon new mages *of the same path*. If you're looking to diversify, water can get you into both Nature (naiad) and Death (Kokythiad) paths at a reasonable magic level, as well as a spell that can get some random paths (Frozen in Ice?). Death also has some summons that can get you into new magic paths, although not at a strong level.

For specific tactical things, see many of the examples above. Simple things can be sticking watchers down with ?Earth to do your patrolling for you, telestic animations to boost Dom by preaching, and so on.