The most important thing: Play you first games in singleplayer.

Look at all items wich you could buy and get a good overview about them. Same for the Demigods, read their abilities and chose the one you like the most. And then just play. First maybe against easy AI, afterwards against normal. Try a few tactics, items only then start to play online. Many people will thank you for that.

You won't make yourself happy if you play in multiplayer at once. You will be killed a alot, many people will be mad about you if they lose "because of you". Not everyone, but many people.

New players often wonder why they are outleveled so quickly in the beginning of the game. Try the following:

When the screen is spinning in, click the item shop. Buy your item and immediately click a flag halfway in the map to get your demigod moving. Choose your skill and select your favor item while on the move. Take over the flag. This can all be done BEFORE the first monster waves hit each other mid field.

Alternatively, buy a teleport scroll/amulet of teleportation and teleport as far out as possible, then hoof it to the flag. Saves even more time and on some maps you can cap 2 flags before the creep waves clash using this tactic.

Flag caps at levels 1-4 are the best source of XP. This tactic is how you get people complaining about running into enemy DG's who are level 4 when they are just about to get to level 2. It can be VERY frustrating to a new player.