The key to creating memorable icons is unity and simplicity. Icons aren’t meant to be complex or have much detail. There should be one overall theme or message, which initiates the unity of the design. Within that theme, each icon should send an individual message.
I provided my set of icons over both a white and black background so you can see the full effect of transparency.
In this design my target audience was young teens looking for indications of the weather. My overall theme was weather, and the individual messages are rain, lightning, overcast/cloudy, sunny, and snow. I created consistency and unity through the same thickness of strokes, as well as the color scheme. Side note: I used yellow and blue for my color scheme, which are primary colors that work well together.
Simple is safe. I simplified my icons as much as possible, by sticking to a sleek and clean stroke for each icon. There isn’t much detail within the icons, but the message is clear. Keeping the design simple adds to the unity as well.
When creating your icons, don’t forget the key elements: unity and simplicity, with an overall theme or message in mind.