Alright let's break down the reel
(This is the reel that got me hired as a mid-level VFX Artist on Hearthstone in 2015.)
  1. I hope to see 6-12 solid pieces in a portfolio. These are recommendations only, but I find 6 can generally satisfy questions of breadth and consistency, and 12 or fewer shows that you can judge and curate your own best work. It's always better to leave them wanting to see more of your work.
  2. A 1.5-2.5 minute demo reel is often the sweet spot. Shorter often makes me wonder how much you can actually make - longer just takes up a lot of time.
    1. Give the pieces some breathing room or 2-5 loops. We won't catch every detail the first time and scrubbing is annoying.
    2. You'll notice my definition of "12" pieces here is... loose at best. You could easily claim this has at least 28 pieces in it. None of these rules are set in stone and VFX and concept art in particular often have lots of stages/sub-components that relevant to the completed piece.
  3. Start and end strong. I don't do this in this reel! My weakest piece is actually first, because this was a Hearthstone-specific reel and I wanted to grab them immediately with the fanart. However, in general you want to start with your strongest piece first and go down from there. How strong the piece at the end is is up to you - I like to go second- or third-strongest at the end so it finishes on a good note. And, again, it's always better to cut a weak piece than make people wonder if you really think that's indicative of your skillset.
  4. Contact info! Start, end, and ideally center. Put it unobtrusively on every piece of media you send it, so it's always readily available.
  5. Credits​​!
    1. Unless it's *super obviously* not yours, credit other people whose work appears in your reel or cite the parts you did (whichever's easier).​
"What about music/audio?"
I pretty much always mute reels immediately, because I want to focus on the VFX.​ (And unmute animation for lip-sync sections, ofc.) I've seen some reels, especially with ambient VFX, use sound to great effect... but you should never assume that they'll hear it.
"Should I showcase 2D concepts in the demo reel?"
It's up to you - to me, proper crediting is the only essential part. If you're proud of how you've realized another person's concept or of the concept you did yourself, show it off! I have the cards onscreen in my sizzle reels for a similar reason - I think that having the mechanics and card art there to reference is the best way of showing what I was translating into VFX. (I don't tend to show concepts mainly just because I so rarely work from one and I find the framing and transitions clunkier than I want to spend my time on.)
"What sort of characters should I be using?"
It's very common convention to just use grey spheres as character placeholders, so you don't really have to do any extra animation at all. I use those lil' animated grey spheres with sphere-hands unless I have a specifically-animated character to use; I'm just not a strong character animator, but I like having a little more context than the static spheres.
In a previous reel I had used a static, posed character model in a grey environment - I dropped this for the spheres in part because I wanted more animation, but mainly because I was moving towards a much more streamlined/greyboxed look.
(The target dummies I just think are cute, do what you will with that.)
vfx reel
VFX Demo Reel (November 2015)

Software : Unity, Photoshop, Maya

Project Spark character models by Fred Pasche, Matt Musante, Matt Gillmeister

Project Spark character animations by Ben Meals, Joe Janca

you're done! that's all you need to make me happy as a hiring manager
All I actually need from a VFX application:
  1. Demo Reel with contact info
  2. Resume with contact info
  3. Boom! You're done. You didn't even need a website, strictly speaking.
Other totally valid ways to display your work:
  • ArtStation (I don't care if you have a custom website or their default portfolio as long as it's easy to navigate)
  • In my opinion, other portfolio/compilation websites are also fair game, but I've seen some devs raise eyebrows at  (I think this is kind of silly, if it's easy to view stuff and all in one place I'm happy, but it's worth knowing that unfortunately ArtStation is generally viewed as more "professional" than, say, DeviantArt.)
  • Yes, that does mean I'm okay with a well-organized Twitter thread of gifs/images, too. (But again, that probably won't be true of everyone.)
  • If you're only sending a demo reel, then just linking directly to the Vimeo/Youtube is great too. Again, it's easy, it's straightforward, just make sure I have your contact info somewhere.:)
Please No:(((
  • Splash/welcome pages - just let me see your work, I beg you. If this were my actual portfolio, I would just have this be what shows up when you type in (Or if I had multiple specialties/sections, I would just link directly to this one for VFX job applications. When I applied to Hearthstone, I even had a /hearthstone page that I linked to in my resume, because it had a reel with Hearthstone fanart.)
  • Small images - I'm fine with clicking to enlarge (especially if I can click/swipe to the next image in fullscreen), . I've genuinely gotten reels that were 240p
    • My website is weirdly narrow so that I can cram all these notes in here. Don't do that! Use the space for big beautiful images!​
  • Password-protected areas are rarely worth it. If you do have some really strong work that can't be made public, pleeease make sure the password is cited in your cover letter, resume, and anywhere else possible. If we can't easily find the password it's very possible we just won't look, because we probably have hundreds of applications left to go through.
Seriously, credit anyone who's work is also being showcased!
I've got everyone credited in the reel as well, but this is also a completely reasonable spot to credit as well. Both is best, imo, since calling them out in your reel helps clarify anything you didn't do, but if you want to link to their work fit's less distracting to do so on the website (and video linking isn't possible on all platforms).
Additional info
Hopefully this is unnecessary, or redundant to what's in your reel's contact card/etc. Reels may get downloaded and passed around without the website (unusual, but it can happen), so it's good to just use this to clarify/reiterate some key information.
Additional VFX Stuff
I think anything after the demo reel is optional and icing on the cake.
I'm gonna add a few examples of what you might want to show off, and hopefully this is helpful, but don't feel like you have to have extra stuff just for the sake of having it!