Rules can always be broken and it's hard to order the “most important”, but I tried prioritizing some foundational rules to creating thumbnails (that you should nearly never consider breaking) here. This is a list is compiled from the top “Thumbnail Tips” videos on YouTube condensed into one list that you can use as a checklist when working on your next thumbnail or evaluating old ones:

Elements:

Elements include words, symbols, people, product photos, and backgrounds. A group of one type of item (like words) counts as one “element”.

  • 4 Elements Maximum

  • Avoid unnecessary items

  • Keep it simple and not busy: Cutout elements or bokeh to blur distracting/busy backgrounds

Text:

  • Quantity: 4 Words Maximum

  • Colors*: Stick with Black or White, Maybe Yellow (* Unless you understand composition and color theory, i.e. you know what you’re doing.)

  • Visibility: Use Outlines or Over a Contrasting Light or Dark Background

  • Size: Keep text LARGE

  • Font: San-serif, Thick/Bold/Block style font, No script/handwritten thin fonts

  • Don’t Duplicate the Title: And see below about creating curiosity

Create Curiosity:

  • Tease,

  • Create Curiosity/FOMO,

  • Communicate Value,

  • Trigger Emotion,

  • Show a Pain Point,

  • State the End Goal, or

  • Tell a Story with Imagery

  • Pixel Blur an element

Pass the Shrink Test / Blink Test / 6-Foot Test:

  • How well can you quickly discern what the thumbnail is trying to communicate or read any text when the thumbnail is small (or from far away)?

Quality:

  • Use Clear, High-Resolution images

  • Professional: Ask yourself, does this thumbnail look “rookie” or would this thumbnail be mistaken for a large YouTuber’s?

  • 16:9 Ratio

Audience Match:

  • Check if the style is appropriate and what your audience would expect from content like yours.

No Man’s Land:

  • Avoid the Lower Right Corner: Avoid anything important in the lower right corner, especially for text, to prevent the duration timestamp from covering key parts of elements.

  • Generally, Avoid the Right Edge: Some overlay buttons show up on the right side. This is of lesser importance to avoiding the lower right corner.

Faces:

  • Consider using your face: Using a face whenever appropriate/possible can improve clickthrough rates.

  • Express Emotion: Happiness, Sadness, Surprise, Fear, Disgust, Anger

  • Look to the Camera

  • Use Close Ups

  • Use the Rule of Thirds: Keep the eyes on the upper 1/3 horizontal line

  • YouTube Face: Although trends are leaning away from the YouTube face, generally speaking, an open mouth, whites of your eyes, and exaggerated emotion do generate higher click-through rates.

Symbols

  • Consider using symbols as an eye-catching element in your thumbnail

  • Arrows: Direct the viewer's attention by pointing to a curiosity-provoking area of your thumbnail

  • Red X and Green ✔: Comparison/Before-After thumbnails can perform really well and the symbols grab attention.

  • Circles: Circling an area is another way to say “look here” as an alternative to an arrow.

  • Punctuation ! ?: Using punctuation as a symbol can evoke emotion, grab attention, and create curiosity.

Branding:

  • Don’t use your “logo”: See above about unnecessary elements

  • Style Consistency: The general look and feel (or your face) is part of your brand that your subscribers will recognize. Whereas elements like logos waste space that could otherwise be used to create curiosity.

  • Avoid Nearly Identical Thumbnails from Video to Video: Videos that use, what often looks like an (albeit well-designed) PowerPoint cover template with only small changes from video to video, may lead subscribers to think they already have seen the video. Podcasts and Livestreams often fall into this trap.

Color:

  • Complementary Colors: Using colors found opposite each other on the color wheel works well on thumbnails.

  • Bright Colors: Thumbnails with brighter colors and higher saturated colors tend to win more clicks.

High Contrast:

  • Use High Contrast: Keeping elements over a light or dark contrasting background, increasing contract on photos, or adding a glow or outline to elements can help make them “pop”.

Clickbait:

  • Good Clickbait: Accurately Portrays the Video, Sets Expectations, and See “Creates Curiosity” above

  • Bad Clickbait: Don’t be Deceptive!

Background:

  • Gradients: When using a color background, generally a gradient (a fade from one color value to another or from one hue to another) is more professional looking as a gradient versus a solid/plain color.

  • Note about Vlog Style Videos: The current trend is to use more natural photographs that depict photographic scenes, yet adhere to all the other guidelines in this checklist, than overly edited (such as cutout images on bright backgrounds) for vlog style content.

Invest Time in your Thumbnails:

  • Given the criticality to your video’s success that a thumbnail contributes, don’t make them a last-minute thought.

  • Create multiple versions

  • Plan Thumbnails before Creating the Video

  • Check the CTR early and adjust

Work In Tandem with the Title and Hook:

  • Assume a potential viewer will either first, or only, see your thumbnail, but let the thumbnail lead into the title, (and ultimately the intro hook) to create a symbiotic relationship that propels a viewer into the video.

Find Inspiration from Competitors:

  • Research other videos covering the same topic as yours.

Compare to Competitors:

  • Would people click your thumbnail over a competing video’s thumbnail? Screenshot YouTube and paste your thumbnail against others to compare.

Catches Attention/Stands out:

  • If you don’t feel the thumbnail stands out enough, go back over all the rules above to find areas to improve