Gamer has been removed
To upgrade your Workbench to max level, you will need the following items:
1 scrap metal, 1 piece of wood, 1 nails, 1 wire, 1 gear, 1 generator.
The only real advice that can be given is to scavenge and explore as much as you can. As well, only focus on upgrading the Workbench rather than anything else; including weapons.