First off, you are going to want to acquire these items to make sure you have as much strategical advantage as possible.
~Full Molten Armor
~Phoenix Blaster / Minishark
~Star Cannon (Will require Shooting star farming)
~Molten Fury w/ Arrows
~30-50 Healing Potions
Alright now that you have acquired all of these items, you are ready to fight the wall of flesh. But wait, before you fight him, you will need to setup a good arena to fight him on. Because the wall of flesh moves from Left to Right depending on where you are, it's a good idea to clear out a flat straight line through hell and build a long platform across hell to give you as much space as possible to attack him whilst staying on the move and dodging his attacks. A good example of a Wall of Flesh battle arena is shown:
Once you have set up a long bridge across hell, you are ready to fight. Go ahead and grind for a Guide Voodoo Doll. Spawn rates can be increased by drinking a Battle Potion or holding a Water Candle. Once you acquire a Guide Voodoo Doll, you are ready to fight. Here are some attack strategies.
~When the battle starts, start shooting at his eyes with the Minishark or Phoenix blaster depending on which one you brought to deal maximum damage to him. If you cannot reach his eyes with the weapon, use the Molten fury or Star Cannon and shoot at his mouth.
~If you are low on health, kill some of the leeches that he spawns, they will drop HP that you may use to heal. If you are too low on HP, use a healing potion or kite him until you regenerate.
~Once the Wall Of Flesh is at low HP, Use the Star Cannon and shoot at his eyes or mouth to deal extremely high damage to finish him off. Keep your distance from the wall of flesh throughout the entire fight to give you as much space as possible to dodge his attacks and attack him yourself.
Once you have defeated the Wall Of Flesh, congradulations! You are now in hard mode. Thank you for reading this guide and have a nice day!