Spacing

One of the more subtle aspects of presentation is spacing.

This can be as simple as ensuring sentences are only a certain width.
It can incorporate space distance between clauses, paragraphs, etc.

Do your best to have text not wrap.

Too, although this clearly isn't a deal breaker:
sentence-wrapping is dissonant.
Dissonance can detract from comprehension.

Certainly it can reduce reading speed at the least.

Take the time to choose the right spacing:
It will increase readibility by something like 5%.

And each of these small improvements will, aggregately, bear fruit.