In general, avoid pure black text on a pure black background. This can look too “default” and the high contrast can be harsh on the eyes. An easy fix is to make the text more of an off-black grey.
If you don’t feel very comfortable choosing colors, you can’t really go wrong by using a single color as an accent in an otherwise black, white, and grey composition.
A great strategy for choosing colors is to find an image or photo with a vibe you like and directly sample the colors from it using an eye dropper tool. Some free tools like Coolors make it easy to pick colors from images.
In many cases, it looks nicer to use a less saturated color than a fully saturated one (more grey and less “pure” color).
If working with text on a colored background, try giving the text just a hint of that color to help them sit better together.
Make sure your text color has enough contrast to be readable on top of your background color. There’s no need to guess about this; color science has yielded a grading system and tools that check the contrast for you: https://coolors.co/contrast-checker/112a46-acc8e5
Layout
Look for ways to align different parts of the design to each other. It creates a sense of visual order and purpose. For instance, if you have an image and below it some text, try aligning the left edge of the text to the left edge of the image. Or if you have a line of text next to a shape, either vertically center the text and the shape, or align the baseline of the text with the bottom of the shape.
Avoid small differences in alignment, color, or size. They look like mistakes. It’s better to have either a bigger, clearer difference or no difference at all.
Be sure to check the scale of the elements of your design at as realistic a zoom level as possible. In software, it’s easy to spend too much time looking at your design while zoomed way in (and making everything too small) or zoomed way out (and making everything too large). Remember the final media.
Use proximity to indicated relatedness between different elements in the design. Elements that are related should be close together, a series of elements that are equally related should be spaced evenly, and space should be used to create separation where things are less related.
Don’t be afraid to be generous with white space in your design.
Type
Word processor documents have taught us to make the line-length of body text too long, resulting in text that is difficult to read. The ideal line length for body copy is generally between 45 and 75 characters per line. A good way to think of this is that body copy should be about as wide as the text in a standard paperback novel or slightly shorter. Look at a printed magazine and you’ll see what I mean.
Body copy generally looks good with leading (also known as line-height) somewhere around 1.5 times the size of the type itself. So 10pt type might have leading around 15pt.
Larger text like headings generally need less leading than body copy.
Remember, most viewers don’t read every word. You can make your text scannable by breaking it into short chunks and being generous with things like subheadings, bullets, and bolded words to help the eye jump from content to content.
Pick a set of type sizes that work well together (known as a typographic scale) and use them throughout your design. This avoids the inconsistent type that results when sizes are chosen manually for each new piece of content.
For digital projects, consider 16px as the minimum type size for body copy. For print you can generally go a bit smaller, often resulting in body copy if 10pt or 11pt.
Consider using type weight (boldness) to create hierarchy and indicate which parts of the type are important. You may want to use size to make things stand out—and you can do that—but you’d be surprised how much weight alone can achieve.
Instead of using two or more typefaces together, consider sticking to a single typeface that has several weights available.