Ok, here are some tips for new players: At first, you make think that dieing to another DemiGod (DG) is not so bad. You lose no money, no experience points (XP), and you only get 30 seconds in "Limbo". So you may think there is nothing to lose charging into towers or several other DGs, because, whats the worst that can happen? Well, the bad news is, the other team gets money and XP for killing you; money they can buy items/upgrades with, and XP that will make them even stronger. When you die to the enemy all the time, it's called "Feeding" them, cause your basically feeding them money/xp.
So, if your healthbar is near half empty, consider running back to a safer place, or use a healing poition (or even use a teleport scoll to get back to safety). Don't take on any towers till you at least level 8, even then only one tower; if two or more can attack you, you will die. Don't take on another DG unless the odds are even, or there is a team member there to help you. Don't let the enemy DG "lure" you back into their towers, where your taking damage from the DG AND his towers too (try to lead them back to your towers to fight you). If your out of mana, think twice before you get into ANY fight with another DG. Remember, run and keep running till your safe or healed; don't "feed" your opponents if you can help it. Try to resist taking one more "swipe" at a DG your running from; odds are, your DG will die, and his "swipe" will heal up the in a minute.
Also, killing minions that come through the portals (often called "creeps") is a good (and much safer) way to earn money/XP for yourself than taking on another DG. Capturing flags gives you xp/money too. Also, if your with an experienced teammate, and he gets in a Fight with another DG, jump in and help, you get xp/money for "Assisting" too. Just be ready to run the second your health gets low.
If you keep seeing enemy DGs that are way higher level than you, or you just can't seem to kill them, you can still help the team by capturing flags, or killing creeps, or even following behind another player to back him up. An enemy DG that is a way higher level than you still has one disadvantge: he can't be everywhere at once, so just be where he "is'nt" and still getting xp/money.
Got to this site to take a look at all the items you can buy before playing a game; plan out what you would like to buy in advance: http://www.scarylogic.com/demigod/items.php
Go to this site to plan out how you want to spend your XP points on your DG before you play a game; like above, have a basic plan on what powers/spells you want in advance: http://www.demigoddb.com/
Also, you can play a solo/skirmish game with special setting to let you learn as you go: Go into options before the game starts (in the lobby) and set the Game Speed for "adjustable". Then use the "-" on the Numpad to turn down the speed to -10 when you want to tool-tip over all the items/skills. Turn it up again to a speed your comfortable with to continue the game after you've read/bought what you wanted.
And you "good" players out there, try a game of 2v1 or even 3v1 agains noobs; it will challenge you, and give the noobs a LOT of expierence (and a chance to beat you too). They might have fun, instead of getting flustered. You can even give them tips while you fight them.