Reduce your samples. I know this seems obvious, but do you really NEED 4,000 samples for your 4k animation? No.
I think this is the first thing people realize when they want to render an animation. But you’d be surprised at how few samples you need to make noise unnoticable, especially when the camera is moving and you have put “#frame” in the seed value to have it change the noise pattern per frame.
Turn down your light bounces. You can find this under Integrator > Bounces. The max you really need for an animation is anywhere from 5-7.
5-7 is already rediculous, start from 1 or two and see if you need any more. Thomas has changed the default lower now as well. If you need more than 5 bounces your lighting setup is bad and you’re relying too much on what you get for free.
Simplify! This one’s under the World tab (the one that looks like pictures), and allows you to make you objects simpler by limiting their subdivision factor. Don’t worry- you don’t have to know what this means.
I don’t use this, not that it’s bad or anything, I just prefer to control exactly what objects get how much subdivision myself.
Turn off anti-aliasing. Anti-aliasing allows you to get rid of jagged edges, but always finds a way to come back and bite you with render times. DO NOT USE AA IF YOU ARE RENDERING A 24+ FPS ANIMATION! Believe me, you don’t need it.
Seriously? Unless you have a retina or some other high-res screen, this is the worst piece of advice I’ve ever heard.
Turn down your subsurf. It’s easy to forget that at the beginning of the project, you made a head with 20 subsurface samples. For rendering. Come on, we’ve all tried it at least once… right?
Exactly. Most models need only one level, or if it’s close to the camera maybe 2 or 3. But a good model is one that is efficient in geometry detail and doesn’t look too different without subsurf than with (model your own bevels, subsurf is just there to smooth the silhouette, not create the curved corners for you). Although if you’re a noob modeler, you can rely on subsurf for a while just to understand everything a bit more, but don’t get too attached and assume it’s always necessary.
Experiment with compositing. To activate this, “pull up” another section of Blender and switch it to Node Editor, then click on the icon that looks like pictures, then enable ‘Use Nodes’. I was once able to get away with making an animation with 20 samples because I did some compositing tricks like blur and defocus. It ended up looking like 100 samples!
Bilateral blur is great for smooth renders, but it fails when you have detailed textures or sculpted models. Instead, render all the passes and blur only some of them (E.g: Diffuse and Diffuse indirect, but not Diffuse Color)
Turn off some things. Don’t need shadows? Don’t waste your time with 'em.
Turning off shadows entirely is a terrible idea. If you’re ok with doing that, why not just render with Blender Internal or even GLSL? A better idea would be to turn off shadows for specific lights, like fill lights. You can often get away with using an AO pass to darken the areas that should have been in shadow from the fill lights.
Turn off ray tracing. In case you didn’t know, ray tracing handles reflections and shadows, but takes FOREVER. If you aren’t using it, don’t think twice to shut it off.
Thought we were talking about Cycles here! Cycles is a path tracing engine, you cannot simply turn it off.
Use the despeckle node. I don’t feel like this needs much explanation, as you are an expert, but you can find it in your Node Editor, under ‘Filter’.
Killing fireflies should first be attempted using render settings such as Clamp and Filter Glossy. Using the despeckle node (or a manual form of it) is really a last resort.
Render on GPU. A huge increase in power and efficiency. Find it in User Preferences, under System.
Of course only if you have a compatible Nvidia GPU and enough vram to fit your scene in.
Bake. You might’ve heard this before, but I honestly don’t know how to use it, so it’s down here.
Good advice, but it means you have to be aware of this from the beginning, make your texture setup in BI, bake it, and set it up in Cycles again with the baked textures.
Change your tile size. If you’re on a CPU, use a smaller size, 16*16 should be fine. If you’re using a GPU, go big or go home- it can only render 1 at a time.
I’ve done a fair amount of research on this - a general rule of thumb: 32x32 for CPU, 200x200 for GPU. Small variations to this don’t make a big difference, it’s not even important to keep it at powers of 2 (16, 32, 64, 256…). I recommend you try my Auto Tile Size addon - it’ll try to figure out the best size based on the compute device, render engine and render resolution (including border renders)