Fire protection, and blast protection.

 

Enchantment

 

Hi, eyese!

When I mine, I have an armour set that I always wear to protect me from the monsters and lava. It also protects me from dieing from falling. The armour has the enchantment "Protection 4" on it, and the boots have "feather falling 4". This armour is all you will need in the mining world. You can literally sit in lava for 30 seconds withought dieing.

 

You die pretty fast in the mining world without armor, but if you wear full nonenchanted diamond armor, it helps a tiny bit, probably like take 1 heart less? Also, if you want to really help yourself, wear full enchanted diamond armor like fireprotection or protection4.

 

or get pyro+ like me so you will never have to worry about lava again :D

 

Also, fire resistant potions are very useful in not catching on fire.

 

@eyesee3 , here is a more precise answer, with some minecraft sciences involved. A full set of diamond armor makes it so that for every second the player is in lava, half a heart will be lost. Basically, in twentish seconds the player will die. It's roughly like that... maybe not so scientific but a good rule of thumb that I've noticed. Trust me, I've fallen into lava many a times!