Qadi Ahmad's Treatise on Painters and Calligraphers
Students often ask me about the sources for miniature manuscript painting technique. There aren't many and only 2 major works I can think of, also heavily biased towards calligraphy (the 'higher' art form). Some excellent info here on manuscript painters and calligraphers - Minorsky's translation of Qadi Ahmad's Painters and Calligraphers: http://www.islamicmanuscripts.info/reference/books/Qadi-Ahmad-Minorsky-1959-cali-paintrs.pdf
(Qāḍī Aḥmad, son of Mīr-Munshī (circa A.H. 1015/A.D. 1606))
Have a read. Scroll down to p. 198 for more painterly info. Not much info on actual practical technique and methods (for that you'll need a teacher and/or practice) but there is info on the materials, some a bit questionable today but there you go! All interesting.