I've only started the game about 3 hours ago, and I've done the quest where I had to retrieve the claw for the shop owner. My bags are chuck full of iron armor and such. Should I sell all of it at Riverwood, or wait until I find somewhere that I can smelt it down?
The first town you get to (*potential spoiler*) is Whiterun. Immediately when you get into town, there is a smelter on the right.
I would recommend either smelting them and then using them to craft or saving them until you get (*potential spoiler*) transmute spell, which turns iron ore into silver ore and silver ore into gold ore. Then smelting them and making necklace/amulets. Either way, this will help you to level up crafting. Once you have made gold jewelry, the price will have increased 10 fold. You can buy iron ore for 6 gold, turn them into gold necklaces and sell them for easily 10x that amount.
If you intend to smith, crafting anything from ingots will help you level up this skill. You can always sell the items you smith after you skill up on them. Or if you plan on enchanting as well, enchanted items you smithed will turn a huge profit compared to the 1-3 g you will get per unit of selling the ore.