The layout of your text will depend very much on the application. A largely text based application may have a screen full of text to read, whereas more graphical applications may try to keep text restricted to small boxes of around fifty words or less. Text is much harder to read from a computer monitor than from a book, and a screen full of small text will be very off putting. If your application determines the fonts, choose them carefully.
Some fonts are more legible than others, particularly at small sizes.
Generally, unlike in text documents sans serif fonts, such as Helvetica, are more legible than serif fonts, such as Times. If your application is cross platform you should remember that font sizes may change on different platforms, for example Microsoft Windows fonts are bigger than the equivalent font on a Mac. Have plenty of white space round headlines Sentences in mixed case are easier to read than those in just capitals. It assigns a number to 128 different characters. These include upper and lowercase letters, punctuation, numbers and 32 control characters such as line and form feed.