https://www.creativeshrimp.com/cycles-x-speed-test.html Cycles x is faster than cycles. Yay.
If you are getting the dreaded cpu out of memory error, try this first:
If you are using cycles, and you render your image while you have the viewport set to cycles view, the gpu is using memory to draw that in realtime. So you set that view to wireframe, and the viewport is now using almost no gpu mem. That mem now is applied to the render cpu+gpu compute. Sometimes that's enough so you can Render with gpu+cpu together again.
Tip- Displacement only works in cycles
A great tutorial of a lot of the settings in Eevee
Good starting place for cycles settings.
Cgboost has good tutorials, and this one describes how to use Eevee.
Grant Abbit has some good tips about Eevee Uses hdri in the world setting.
Cgboost one of my favorite Blender channels has some good cycles rendering tips.
SouthernShotty has good news about getting faster renders and ai Denoiser Fyi Blender 3 should have the new denoiser.
Blender guru has some more advanced settings techniques for cycles.
He uses several tricks and tips he shares to Add in fake hdri image lighting, radiosity shadows. Great tutorial and fantastic results in Eevee.