The overworld is the initial dimension of the game Minecraft. There are a number of important resources you will want to obtain in the overworld before making your way to the next dimension: the Nether.
The main resources you will be looking to obtain are tools that allow you to break blocks quickly and combat mobs, a bucket to build a nether portal and lots of food to regenerate health and keep sprinting. Other useful materials can be blocks to build around and a shield/armour to survive taking hits from hostile mobs but when trying to go fast, these can be lower priority. The fastest way to obtain these resources are generally from overworld structures and which one you decide to go for should depend on the seed you are given: