Clear design is something you can practise when you look at signs, brochures, advertising, anything written or printed. The first step in writing is to decide who will be reading what you write. Who you write for will influence every decision you make about style and layout. What may be fine for an advanced reader may completely block a beginning reader, whether that be vocabulary or type style. For instance, very basic readers will need a lot of white space, but more advanced readers can handle densely packed text.
Typeface is the style of lettering.
Some examples are shown below. There are a number of good choices. I use the typeface called Times Roman or one of its relatives like Times New Roman, Garamond Antiqua, Toronto, or Palatino. Times Roman is the easiest typeface to read, according to scientists. Here are some typefaces to compare.