Ok Be mindful of these tips.
Do not use QMC. QMC calculation is the most exact yet the slowest.
When using IR engine (say-5, -3) calculate faster but be aware of light leaks.
when using IR engine, set up at least one Vray rectangular light (invisible) beyond the camera with low multiplier. This will act in certain way as fill light but at the same time areas will smoothen your image. (see my WIP tutorial at asgvis on this). Edit: adjust also in order to prevent artifacts set the QMC adaptive sampler to 0.85.
Use Light Catche as your 2nd engine. the Default 1000/ samples .02 size/ make it 600 and samples 5 for quick review (a bit blurry but quicker) for final use .02 size and higer samples . Be sure you tick the glossy box something.
Now its always advisable to save your IR and LC and reload them. so if you rerender again your image, vray wont calculate those things anymore and it will go direct to rendering. Also saves on the memory used in the final render process...very advised for HiRes
Under global switches, turn off default lights and hidden lights. Its better always to override sun's parameter.
Image Sampler... Adaptive Subdivision is often quicker than Adaptive QMC (most of the time, but not always. Adaptive subdivision with -2,1 is very quick.
Antialiasing off. jsut use it for final render. If you are using Adaptive subdivision of -2,1, antialaising on is still quick.
NOW this is the culprit... QMC noise threshold.. the lower the noise threshold the longer render time.. use default for test. final is may .005-.007
Lighting. the more lights yo have the longer render time
Blurry reflection renders longers. the higher subdivision the more longer time
Shadows... more subdivision more smoother, but longer render time
BUMPS are easier to use, takes shorter time to render than Displacement. jsut use displacement if necessary.
For final render, re-start your computer. this clears up memory from all of the different programs that wind up running. Damien of sgvis suggested even, if you really want to save as much memory as possible, then go through the programs that are loaded at startup and remove the ones that are unnecessary.
Alway purge your file. all thsoe extra files takes space of yur memory, Damien added explode as many components as possible. Nested components might cause issues, and components also take longer to work with when reading the scene from SU. (dont explode the faces you want to apply displacement, displacement wont occur) displacement will only occur on only on Group objects or faces)
Dont use caustic. calculation of caustics takes longer
Glazes. avoid using double glazing.. cause refraction will be calculated many times. (But if you use sometimes single glaze, refractions are not really correct)
Translucent materials takes looooooooooooooooong time to render.
turn off sketchup shadow, outliner and all those extra windows in Sketchup during render time. (outliner is a big culprit)
Use track mouse during render time. (Only test an area that you are concerned about- dont overdo it) point your moude to the area you want to see first. it will definitely save time.
there are some more of course.. but i think 20 is enough.
Now again its render time against quality. If you want super quality image, it will really takes longer render time.
