Efficient Hellevator design
Take a pickaxe and start digging a shaft 2 tiles wide. If you find a cavern, wall it off on both sides if you want to avoid being damaged by enemies on your way down. If you don't have wings/rocket boots/a jetpack, build a wide wooden platform a dozen or so levels below hell's ceiling. If you don't have a lucky horseshoe, shoot your grappling hook towards the platform, and you will not take fall damage. You can also break your fall by grappling to the walls. Look at the minimap to be ready for the end of the trip. You can also use a 3 tile high pool of water or some rope to break your fall.
As for the way back up, 2 words: Magic Mirror.
You can also try making a rope hellevator by placing rope in a vertical line down from your house and into Hell, if you want a solution that takes advantage of 1.2 features, but the time it will take to build is quite long and it provides no benefits except for making sure you won't take fall damage on the way down (it's also helpful if you don't have a magic mirror, but by the time you start exploring Hell, you really should have one).
Dealing with obstacles:
Pre-hardmode you should not come upon any types of rock that can't be broken with a good metal pick. However, you will likely have to deal with several pockets of magma. Water turns magma into obsidian, and you will likely have a lot of water in your hellevator as a result of breaching underground lakes. Let the water turn magma into obsidian and dig through it as long as you have the water to turn the magma underneath into more obsidian. If you don't have a lot of water, it can be helpful to use some of the materials you picked up to build a few walls on the sides of your hellevator so falling water doesn't escape the shaft. If you run out of water, move up, find an underground lake and mine a tunnel from it into your hellevator. Alternatively, you could just chug an Obsidian Skin Potion, a single bottle should give you enough time to bust through, though the Fireblossoms required to craft one may be hard to come by without reaching Hell first.