For spells you want to use ignite for 3v3 but switch to teleport for 5v5, you want to be in the fray as long as possible without dieing so return to base if your low on health but get back quick to, pantheons special helps with this a lot.
For mastery tree you want to focus on damage and heath and armor.
For your skills focus on the spear and Aegis because these will be your stunning and damage dealers. Most people like Heartseeker but i only like it for minion killing so i use it last. jump from the spear to aegis then once skyfall comes up level that up and everytime you can level it up do. Warning! i tent to be suicidal with Grand Skyfall because i see a bunch of enemies bunched together and i get ansy, warn your team before you go suicidal, i dont but you should.
For runes ignore what i did i just filled in random ones so go for heath and armopre and attack speed.
For idems its pretty self explanatory, you start with the the Ruby because its part of the heart of gold witch will get you all your money and you will need it. Then you go for movement speed and attack speed with the grieves. then you go 1 sunfire cape to get a ton of heath and aoe damage. this is when we go from a tank build to a semi decent dps, this surprises most people when the dont think you do a lot of damage and then bam there dead and confused. the bloodthirster for heath steal to keep you alive longer and then the black cleaver because its epic. you end it with another sunfire cape though the game will most likely be over by now if it isent it soon will be. if your game isent over yet then 1 you have been playing to long and 2 your crazy, but if this happens then sell the heart of gold and buy something for attack speed or damage, id go for a trinity edge.