Some principles on Arraiolos: 
(1) Everything ´happens´ on the right side. The wrong (or the reverse) side is ´perfect´ as all beginning and ending of a thread in the embroidery is hidden on right side under the stitches already done. 
(2) A single stitch has always 3 overlappings of the thread on it. Sometimes 4. 
(3) A ´filling´row is always from a different direction as its previous and the one following.
(4) Rows are always worked across the longest side of the rug. If you working a square cushion, for example, choose the botton of the motif to work horizontally from it. (See picture of Pag.5 below as they speak of "sentido do bordado").

Revista Clássicos de Arraiolos Edição 103 - Março 2009
Editorial Nascimento - Tuttirev Portugal

This is the continuation on "Curso de Arraiolos - 4a Parte".
This is the best explanation on Ponto de Arraiolos I have found.
That´s why I´d like to share it here.