After using blender for years and optimizing it, these are my default settings now
render should be 512 iterations max for my settings, and 128 if I want to be lazy, with 256 about in the middle, everytime you want a bit more smoothness, you have to double the number, I just happen to use base 2 numbers because I've memorized them for many things.
Drop you max light bounce as much as possible, I go as low as 2 or 3 for diffuse and glossy, I set my total to which value is highest, and transparency, i would never go below 4 because windows and glasses tend to go black, but I found 12 was good for keep see through objects clear enough, and I use transparency alot for clothes... you may notice some blackness with hair if it uses lots of layers with transparencies (ie after 12 transparent objects it will start rendering black due to max light bounce being exceeded).
I cap indirect light at 10 to minimize the amount of noise in an image, if you really want to force the image to be clean, you can set this to 1.0 and use filter glossy at 5.0, but i found I didn't need it, and it slowed things down a bit. turn of caustics is a must. I have an 8 thread CPU, so I max out at 7 threads so that my Computer doesn't freeze or slow down (so I can continue to brose the internet or watch videos).
I use both CPU and GPU sometimes, with 128 being a good middle ground for tile size.
And make sure you are using denoising when possible (in the compositor, see below). Before denoising, it wasn't uncommon to use >2K iterations to get a smooth image, and its why 256 is good enough for me.
edit: if you look near the bottom, I also have the old fashion form of denoising turned on, I like to compare the results, but I suggest turning this off to speed up rendering,