Important Notes

Organize your files! It sounds boring but it will save you a ton of headache in the long run!
I would recommend creating a dedicated folder for VRChat project assets, and splitting the assets up by first:
Avatars
Worlds
And then:
Textures
Models (if a texture goes with a specific model group the two in the same folder)
Prefabs
Shaders
I would recommend organizing your textures by type, similar to how they are categorized in texture websites like https://ambientcg.com/.
What’s important is that the organization works for you; you can adjust it however you like.
Name your files descriptively! You should be able to know what a file contains without having to open it!
Hitting the Tab key in a text box jumps to the next text box!
Reset GameObject transform
On the transform component of a GameObject, click the (gear on the top right) and click reset.
This will return the object to XYZ position & rotation to 0,0,0, and the XYZ scale to 1,1,1.
Alternatively you can just reset the position, rotation, or scale individually via the same dropdown.
Copy & Paste Components
Click the gear on any component
click copy
click the gear of another component
click “Paste as New”
If working in Blender, there are many addons (free & paid) that can speed up your workflow!
3rd most important tip: if you are creating something custom, use reference photos! You will not be able to create something in 3D from memory as quickly or as good as you would from a reference photo! There are many subtleties and details you forget!
2nd most important tip: if there’s something specific you’re trying to do, don’t try to figure it out yourself, look it up! Speaking from experience, you will likely become frustrated and do it in a suboptimal way. There are many tutorials and answered questions that will help you immensely. If you can’t find the answer you’re looking for, post a question! It’s almost certain other people have it too and that someone has the answer. Even experts ask questions.
And the #1 most important tip: if something goes wrong in Unity, READ THE CONSOLE!!!
Unity Tips