Limit your polycount to minimum as much as possible. The more polycount, the slower the rendering.
If you are using Vray, always proxy the ones with high polycount.
Don’t put too many subdivisions on your shadows (as much as possible).
Remove unwanted objects from your scene
Don’t use giant resolution textures. I.e. If you render your final image at 3500px you don't need more than 4000px image anywhere.
Material wise: avoid using too much glossiness and highlights. A simple diffusion, bump and reflection(with .95 – .75) will do. Try to use your own materials rather than prepared. You will have better control on them.
Use high polygon objects only when they are close to your camera.
Know the difference between copy and instance… Simple but effective
Get rid of the undo window, especially commands on the list that eat up memory…
I always shutoff my antivirus while rendering (or don’t install one at all).
Be wary of iteration levels when making curves/mesh smoothing.
Caustics are a time killer. It's up to you if you want to drink and eat and sleep until the rendering finish.
Be wary of glossy reflection and frosted materials..(case to case basis)
Instead of using dof in physical cam, Photoshop can do the trick with zbuffer channel or plugins like Alien Skin’s DoF and DoF Generator PRO by Richard Rosenman.
Post process could be short the rendering workflow, professional composition programs like Autodesk’s Combustion, Photoshop, After Effects, Nuke, Fusion… could help you a lot.
Irradiance and Light Cache (save to file), skip the computation when using the same sets and scene over and over again.
Before you place all the shaders, first try to override the materials in the rendering parameters (global switches) to make sure all polygons are modeled correctly for test rendering so that you know the types of shaders you placed individually and you can trace easily which materials could possibly cause the rendering longer.
Too many lights can also cause overkill of the rendering.
I prefer ADAPTIVE DMC rather than Adaptive Subdivision…
Check your Raycast Parameters too...Like render region division, region sequence etc.
If you’re using Vray displacement mode, try to limit the area of 2d mapping and setup for it eats up a lot of ram.
Use 64bit Max
Attach those objects – 3ds Max is much more efficient working with 9000 10k polygon objects than 200,000 1k polygon objects. Attaching all the components that are not being individually animated adds a significant amount of speed and flexibility to the scene you’re working on.
Geometry Proxies – Ah yes, my new favorite tool! A geometry proxy is an optimized piece of geometry that is designed to load and render much more efficiently in specific render engines such V-Ray.
Bitmap Proxies – Bitmap proxies are a great way to minimize the amount of RAM you expend on a scene.
Work Locally and Incremental Saves – You must wonder why… Well, as you save to the network share, you can run into some traffic issues which can occasionally cause crashing and corrupted documents.
You might want to check the multi-threading option if you use a dual processor.
Use Rendering Region: render only what interests you. From time to time check your shaders, verify the little differences and quickly find the result you’re looking for.
Do not add Glossy effects. Add it only when you think that the scene works fine.
Geometry – scenes with lots of objects and/or triangle counts require more memory to render. There are several ways to reduce this amount: -Adjust the raycaster settings in the System rollout (reduce Max. levels, increase Min. leaf size, increase Face/level coefficient and switch from Static to Dynamic Default Geometry).
Displacement mapping – objects displaced with the 2d displacement mapping method may require a lot of RAM to render, especially with large displacement maps. If this is the case, use the 3d displacement mapping method. Also, if you have several distinct displacement modifiers with the same displacement map, it is better to replace them with one modifier applied to all the necessary objects. This is because each modifier will take RAM for the displacement map, separately from other modifiers, even if they have the same map.
Bitmap filtering – Summed area filtering uses much more memory than Pyramidal filtering. Use summed-area filtering only for smaller bitmaps.
Shadow maps – these may also take up significant amounts of RAM. Again, these are managed by 3dsmax and VRay has no direct control over their memory usage. To reduce memory usage, you can switch to raytraced VrayShadows instead.
Image buffer – large output resolutions require a significant amount of RAM to store the final image. Additional G-Buffer channels increase that amount. There are several ways to reduce this amount: -Use the 3dsmax Bitmap pager, if you render to the 3dsmax default VFB. -If you use VRay’s own VFB, use the Render to VRay raw image file option and then use the VRay raw image file viewer to convert the final file to a different format.
Image samplers (AA) – the image sampling algorithms of VRay require some amount of RAM to hold all the data for the sampled image. This amount can be quite large, depending on the chosen bucket size and sampling rate. To reduce that amount: Reduce the bucket size. -Switch to a different image sampler – for example, the Adaptive DMC sampler uses less RAM than the Adaptive subdivision sampler.
Even though you select the VRAY VFB as your output, the 3dmax VFB is still created and thus takes additional memory. If you want to reduce that memory, you need to uncheck the “GET RESULUTION FROM MAX” option. Set the 3dmax resolution to lower value like 100 x 100 and then choose your real output resolution in the VRAY VFB option.
Inspect your scene -were there lots of unused polys? Were there alot of models that only clatter the scene but are not viewable on camera? Were there lots of unused materials on the editor? I mean, sometimes we think that our render setup is hampering the rendertime, but if we just inspect our scene, the things mentioned above are factors that affect a lot.
Sometimes our model in autocad was located far from the axis origin; this happens quite often. Then once we link it up to our rendering program we just let it as it is. This also prolongs the rendertime when executed. Bring it back in 0,0 axis position while still in autocad.
Overlapping of Models and meshes. – A scene with many of these will take longer to render. You need to tweak your setting into higher so as to cover up those splotches.
Rendering Large Images – rendering a large output image takes longer when rendered as a whole. Use alternatives like split rendering or some render plugins like Super Render – where, in the scene, it will be subdivided into bucket window and then automatically combine them after the last bucket.