Basically you need a good weapon from the AH for about 10-50 k and some good gear from Hell. Depending on your class you just need to farm good 57 gear, because as Deamonhunter or as Wizard (damge dealer or DD) it is completely normal to get oneshot at least in Act 2 and above, so just adjust your playing style.
As DD your main goal is to increase your DPS until you can kill Skeletons etc. with 1 to two shots. As tank you need to boost your defense until you can survive melee combat against normal monsters.
You cannot kill every Elite in Inferno, as there are very very nasty combinations. Mages struggle with Reflect Damage especially in combination with Increased Health. So if there is an "unbeatable" Elite either restart, avoid him and try to get your buff somewhere else or skip him by running him into a distant corner and dying.
If you are unable to do the above ask in the chat if someone can help you with one or two Leoric runs. Currently many people are stuck with act 1 as you need really good gear for everything above.
If you have friends that are level 60 already, just ask them for some items or if you can join on some Leoric runs. Usually a good level 60 damage dealer can easily output the required DPS.
If you are a tank and no one is willing to tag you along then ask in general chat for cheap gear. Many people, me included, have a ton of decent items that they cannot sell in the AH because of inflation and limited auctions. If you are willing to buy for 6-7 times the vendor price people will sell you cheap stuff so you can at least start Leoric runs yourself.
As already stated you could also wait for the patch that reduces the gap between Hell and Inferno.