I have 100 smithing now.
Easy way to level up smithing: grab as many iron ingots or iron ores (to turn into ingots) as you can, and buy up as many leather strips as you can. Alternately, hunt a lot of animals, take their hides to the tanning rack and turn em into leather strips.
Now take all those ingots and leather strips and make as many iron daggers as you can. You will level up fast and easy. Don't bother trying to smith more advanced items, because you don't level up any faster.
Once you hit 90 smithing you can make legendary armor and weapons. Make sure you get the perks so you can make daedric stuff.
And if you level up your alchemy and enchanting trees you can enchant stuff to give you smithing bonuses and create potions to make your smithing more effective. Totally broken.
However, leveling up enchanting and alchemy takes longer from what I can tell.