Clear design should…

Above all, be useful. Get the user's job done and get out of the way as fast as possible. But also while at it, it should…

Be unambiguous.

Only one possible interpretation should exist for every design element.

Be predictable.

Design elements should help people accurately and consistently predict what happens when they interact with your product.

Be helpful.

Design should help people answer all these questions:

Where am I?
How did I get here?
What can I do here and how do I do it?
Where can I go from here?

Be accessible.

Design elements should adhere to AAA or AA accessibility standards because it makes design better overall for everyone

Be aesthetic.

As a whole, the functionality of the product should be well executed. After that's achieved, there's no excuse to not make the product aesthetically beautiful

Be honest.

As a whole, the product should be free of jargon and should only promise what what it can achieve for the end user. No less, no more.

Some useful heuristics

I think of these every now and again. Not too hard, and not too often.

Name	Description	Example or usage
Anchoring bias	People rely heavily on the first piece of information they see	Explain the value your product provides in one sentence, not what your product does
Progressive disclosure	One bit of info at a time, as needed	Start simple, increase complexity as you go along
No walls of text	People don't read online, they scan for words https://www.nngroup.com/articles/how-users-read-on-the-web/	Don't hide critical information, surface it with highlights.
Peak/end Fallacy	People tend to remember the peak (positive or negative) of an experience and its end.	Memory is unreliable. We remember how something started, the strongest emotion we felt, and how it ended. Excellent design accounts for this
Confirmation bias	People find evidence that confirms what they think
Feedforward	When people are able to predict the outcome before they take action	Call it what users call it. Buttons hide actions that exist behind them. Views (screens) hide outcomes that are possible
Pseudo-set Framing	Tasks that are part of a group are more tempting to complete	Complete profile. Create community. Increase reputation.
Spotlight Effect	People erroneously believe that they're being noticed more than they are	Everyone is thinking about themselves most of the time. Design for that or around that
Goal Gradient Effect	Motivation increases as people get closer to their goal	Progress bars work
Von Restorff Effect	People remember things that stand out	When multiple similar objects are present, the one that differs from the rest is most likely to be remembered. Especially useful in guiding the user through a specific flow - make important info stand out (like CTAs)
Social proof	People adapt their behavior based on what others do
Familiarity bias	People prefer things they already know
Loss aversion vs. equal gain	People prefer to avoid losses than win equivalent gains	Saving what you have is more important than gaining what you don't, to most
Reciprocity effect	People feel the need to reciprocate when they receive something	Give value before asking for value
Survey Bias	People tend to skew answers towards what’s socially acceptable	Also, users change their behavior when observed
Priming	People remember the previous step/info which sets expectations
Cognitive load	Amount of effort required to complete something	Just-in-time complexity helps people move through even complicated context
Pareto Distribution	For many events, 80% of the effects come from 20% of the causes	20% of platform users typically generate 80% revenue
Hick's Law	The time it takes to make a decision increases with the number and complexity of choices	Just try picking one of these to use
Miller's Law	People only keep 7 (+or - 2) items in their working memory	Shorter sentences are easier to recall. 5 or less nav items are easier to learn/remember. Text containers should have max-width: 680px with font-size: 16-21px (NOTE: ideal font-size for maximum legibility is 21px)
Proximity Effect	Elements that are close together are usually considered related	Group settings by their function to help people configure them faster
Feedback Loop	When people take action, they expect feedback to communicate to them what happened	Empty states, error states, success state, loading states are all opportunities to show people that they are in control
Occam's Razor	Among competing guesses, the one with the fewest assumptions should be selected	Especially useful in user research. Start with behaviors that you have the fewest number of assumptions on
Tesler's Law	Certain amount of complexity cannot be avoided	Simplicity for its own sake passes decision making to the end user (which increases friction)
Jacob's Law	People spend most of their time on other websites/apps	Don't re-invent common interactions like signup/login - your product should feel similar to others
Doherty Threshold	Productivity soars when a computer and its users interact at a pace (<400ms) that ensures that neither has to wait on the other.	Apps/websites have to respond to users within 400-900ms, otherwise they might not be used
Serial Positioning Effect	People tend to remember the first and last items in a series.
Zeigarnik Effect	People tend to remember and come back to unfinished tasks	Especially useful in onboarding users to complex products that have a steep learning curve
Fitt's Law	The larger something is, the easier it is to hit	The amount of time required for a person to move a pointer (e.g., mouse cursor) to a target area depends on the distance to the target divided by the size of the target