If you are making mitred squares for the first time, try doing a square using instructions for the A1 square in this pattern.

Use a smooth non textured 8ply yarn with 4.00mm needles before tackling with the boucle.

Suggested yarn:
83% Australian Alpaca, 17% Synthetic Binder
Alpaca Ultimate Boucle

(50g/1.76oz,122m/133yds, 10wpi, CYCA#4; medium, worsted weight, Aust equiv. 10ply) x 4 balls in colours black (A1), Charcoal (A3), Ruby (A4), x 3 balls in colour Berry ix (A2), and x 2 balls in colour Purple mix (A8).