How should I prepare for these things? Good advice: Base strategies, weapons and accessories, etc.
This is more answerable in addressing what the major shifts are going to be in defeating the wall and moving forward.
The main thing is that corruption and hallow are going to start spreading around your world. You want to make sure that your base is protected against this so it remains under your design/control for what spawns where and the materials you can harvest there. You can do this with sun flowers on the surface but to keep the stone from changing and such you really want to dig out a 5 wide tunnel around your base or have built up in the air.. It can get really dicey in hard mode if the corruption or hallowed spawns start happening at your base.
Secondly is going to be your tools.. make sure you harvest and farm what you can now because it will be harder once you get into hard mode. Go for the Hellfire armor/tool set or fish for their tools and such as they will both let you get the hard mode ores but you can obtain them outside of hard mode.
Lastly, as for the wall of flesh.. You really just want a very long platform. If you are unsure of your capability against the wall of flesh then just build a very long platform. Being able to run backwards is essential as if it catches you it will do a lot of damage.. and if you try to run away you instantly die. Build up your defense, get some mobility objects (mostly talking about the running boots from chests or fishing here) and then a solid plan of attack be it magic, ranged or even if you are daring, melee.
That is basically it.. This is an important change in your game but it is not as daunting as people think it is.