The Arab culture values highly the aesthetics and meditative spirituality of calligraphy, so it is unsurprising that the mastery of handwritten Arabic is seen as an indicator of a dedicated, serious student who merits respect. Writing Arabic by T.F. Mitchell is a comprehensive approach to Ruq'ah, the handwritten script most widely used throughout the Middle East today. Although each of the 28 Arabic letters can have different forms when they are isolated, initial, final or medial (i.e., between two other letters), there are even differences among the standard forms of individual letters for attaching to different letters, e.g., the medial form for any given letter can have variations to accommodate different letters following it. Mitchell not only explains this, he shows examples for the student to analyze.
Mitchell's book feels dated: The Roman text is typewritten while the Arabic is done by hand in (I believe) reed pen & ballpoint pen, as appropriate. It looks like—because it is—an academic manuscript from the 1950s. The text is designed primarily to teach the beginning student in Arabic how to write ruq'ah (رقعة) script with a reed pen. It teaches the same skill for ballpoint pen as something of a decently-executed afterthought. I used it successfully for the latter purpose.
The first chapters are tedious, but not difficult. They can be managed with spacing & patience. Later chapters move more quickly. Patience in the first two chapters will make the final ten easy work. While the book was designed to teach calligraphy with a reed pen, I think that other calligraphic pens (or, in fact, a Sharpie marker) would work equally well. Cursive, ballpoint equivalents are given for all examples, & it was these that I used. I imagine that most modern students will be more interested in learning how to write good Arabic for day-to-day purposes, rather than calligraphy. The book is adequate for this purpose. It has a good number of exercises for each lesson, which are both enough to help a student improve, but few enough that they do not get boring.
The book ends with several appendices. For me, the most useful among these was a set of ten examples, written in phonetic transcription, reed pen ruq'ah calligraphy, & ballpoint pen ruq'ah cursive. I used the transcription to write out a cursive copy, & then compared it to Mitchell's version.
The one section in which I felt that there was not adequate information was that on the connection of lām to a following mīm.
A student who does not yet know how to read Arabic & who is primarily interested in learning to read will probably not find the book as useful: It contains no naskh (نسخ) script, which is the standard for printed Arabic, just as ruq'ah is standard for handwriting. I do not know how useful the book is for a student of Arabic calligraphy. However, for a student of Arabic who can already read, this book can help you to fairly quickly elevate your handwriting to a mature, local style. Good penmanship is not the most important element of learning a new language, but it is far from trivial.