Use Jakob Nielsen’s general principles for interaction design. They are called heuristics because they are broad rules of thumb and not specific usability guidelines.

From the book Cracking the PM Career:

#1: Visibility of system status The system should always keep users informed about what is going on, through appropriate feedback within a reasonable time. #2: Match between system and the real world The system should speak the users' language, with words, phrases, and concepts familiar to the user, rather than system-oriented terms. Follow real-world conventions, making information appear in a natural and logical order. #3: User control and freedom Users often choose system functions by mistake and will need a clearly marked "emergency exit" to leave the unwanted state without having to go through an extended dialogue. Support undo and redo. #4: Consistency and standards Users should not have to wonder whether different words, situations, or actions mean the same thing. Follow platform conventions. #5: Error prevention Even better than good error messages is a careful design which prevents a problem from occurring in the first place. Either eliminate error-prone conditions or check for them and present users with a confirmation option before they commit to the action. #6: Recognition rather than recall Minimize the user's memory load by making objects, actions, and options visible. The user should not have to remember information from one part of the dialogue to another. Instructions for use of the system should be visible or easily retrievable whenever appropriate. #7: Flexibility and efficiency of use Accelerators—unseen by the novice user—may often speed up the interaction for the expert user such that the system can cater to both inexperienced and experienced users. Allow users to tailor frequent actions. #8: Aesthetic and minimalist design Dialogues should not contain information which is irrelevant or rarely needed. Every extra unit of information in a dialogue competes with the relevant units of information and diminishes their relative visibility. #9: Help users recognize, diagnose, and recover from errors Error messages should be expressed in plain language (no codes), precisely indicate the problem, and constructively suggest a solution. #10: Help and documentation Even though it is better if the system can be used without documentation, it may be necessary to provide help and documentation. Any such information should be easy to search, focused on the user's task, list concrete steps to be carried out, and not be too large. Beyond those 10 heuristics, here are some common guidelines to remember: Limited attention: Real users pay much less attention to your product's UI than you'd guess. People subconsciously ignore big flashy banners and anything else they think are ads. They won't read long paragraphs or even sentences of text. They can get interrupted and distracted at any moment. If the main callto-action is not crystal clear, they'll give up. Whitespace and proportions are important: Whitespace and proportions make a huge, visceral impact on how people react to your product. Too little, and it will feel cramped and difficult; too much, and people will feel like the app is oversimplified and slow. It's almost impossible to get useful feedback on a design when these details are off because they create such a strong negative reaction. Accessibility: About 4% of the population is partially colorblind, and about 2% of the population has another visual disability. 5 Testing your product for screen readers and color blindness are easy ways to avoid excluding some of your users. Don't rely solely on color or images without alt-text for any important part of your UI. As a bonus, when you design for accessibility, people without disabilities often benefit from the design as well, a concept called "universal design." 6 Consider reviewing your existing product with these guidelines in mind. Where do you follow them? Where do you break them?