Here is my version of the basic instructions for mitered crochet square.
HOW TO Mitered Crochet Squares using single crochet:
1. Decide what size square you wish to make.
2. Start with a chain double the length of one side of the square.
3. For a 3in square, length of chain needs to be 6in.
4. Even number of stitches plus one stitch for centre.
Simple Crochet Mitered Square
ABBREVIATIONS: USA (American) Crochet Terms
ch = chain, st = stitch, sc = single crochet, sc3tog = single crochet 3 stitches together.
Row 1: Ch25.
Row 2: Ch1, sc in 11ch, sc3tog, sc in next 11ch. Turn. (23sts)
Row 4: Ch1, sc in 9sts, sc3tog, sc in next 9sts. Turn. (19sts)
Keep decreasing in same manner for each row as follows:
Row 5: Ch1, sc in 8sts, sc3tog, sc in next 8sts. Turn. (17sts)
Row 6: Ch1, sc in 7sts, sc3tog, sc in next 7sts. Turn. (15sts)
Row 7: Ch1, sc in 6sts, sc3tog, sc in next 6sts. Turn. (13sts)
Row 8: Ch1, sc in 5sts, sc3tog, sc in next 5sts. Turn. (11sts)
Row 9: Ch1, sc in 4sts, sc3tog, sc in next 4sts. Turn. (9sts)
Row 10: Ch1, sc in 3sts, sc3tog, sc in next 3sts. Turn. (7sts)
Row 11: Ch1, sc in 2sts, sc3tog, sc in next 2sts. Turn. (5sts)
Row 12: Ch1, sc in 1sts, sc3tog, sc in next 1sts. Turn. (3sts)
Row 13: Ch1, sc3tog.
You can change colour after every 2nd or 4th row.
You can make your mitered squares individually or "join as you go". If you plan to create different patterns with the squares then you will want to join your squares later.
Have a play, and have some fun!