Read the tips for noobs it's a pretty good summary. Plus look in strategy forums for ideas on your favorite demigod. There's even a thread someone's posted listing good items and useless items. Unfortunately the developers never rid the useless items, but then on some maps some useless items become useful... and Aura items/skills/favor would be even more useful in 4v4 and 5v5 games but alas, the game never got the momentum to fund the little people working 18 hours a day to make an awesome game into a perfect game.
But unless you're in a real high mana map like in1 mentioned, your demigod's mana regen is quite low. So to have a +35% regen is garbage useless. Take a look at sedna for example: at a mana regen of 3 per second at the start (unless you got a mana regen favor item) You're talking an extra 1 mana per second. That's shit. Useless. What are you gonna do with that extra 1 mana per second. Have you got 5 minutes to stand around waiting for enough mana for that extra heal while unclean beast is eating your face off? No, you'll be dead. If the item was +200% regen I'd consider buying it MAYBE.
Even torchbearer with the highest regen stat for mana (depending on mode - fire/ice) it's about 4. So still the buff is 1 per second. Bah a waste of time. Scaled helm is cheaper and gives you +5 and a bigger mana pool. And no, it's still not worth stacking visor on top of other mana regen items. You're wasting a slot where a buff to armour, health, speed, or damage could go.
Stupid helmet.