Make a copy of Irene Wellington's teaching sheet, C84.68 writing directly with a broad edged pen. You could try simplifying the serifs to give the form a more contemporary feel.
Although Johnston taught himself calligraphy it is worth saying that joining a calligraphy class will speed up your learning process enormously. Actually seeing someone write can convey more information than pages of reading. Such classes are also invaluable in allowing you to discover the resources of your own region and where to buy supplies and paper, as well as providing encouragement to you as you take your study of calligraphy more seriously.