This is going to be obvious and dumb for some of you, but I really had no idea how to do this until I did it accidentally on my own. Now I can't say that I don't like iced tea, but as with many other things I'm just picky about it and prefer to make my own.
Start by buying a decent quality of tea. Stash, Republic of Tea and Trader Joe's all make fantastic teas that can seem pricey but are incredibly cheap per cup. My current love of Stash Jasmine Green Tea, and it was about $4 for a box at Price Chopper.
Brew your tea in about 2 oz hot water. If you want your tea sweetened, sprinkle the sugar in at this time. This is actually pretty important because the sugar will dissolve and later be evenly dispersed through the drink rather than having grainy, super-sweet dregs at the bottom of unsweetened tea.
Don't over-steep the tea or it'll get bitter. Ick. Anything in the general time range listed on the package usually works fine for me. Remove the tea bag.
Dump in 8 oz ice and water. Crushed ice works well. I fill my cup all the way with ice, add as much water as will still fit, and then the ice finishes melting right as I'm at the bottom of the glass of iced tea.