Here's a pattern I've been working lately:
I've been using double strands of worsted-weight yarn with size 13 needle.
Cast on 115 sts
K1 P1 K1 P1 across
K1 P1, repeat across
This is called the Seed stitch. Do this for 12 rows.
Row 13 - K1 P1 K1 P1 K1 P1 K across until 7 sts are left, K1 P1 K1 P1 K1 P1 K1
Row 14 - Seed st for the 1st 7 sts, then Purl 99 sts, Seed st for the last 7 sts.
Repeat rows 13 and 14 until it's about 60" long. Then do the Seed st across all sts for 12 rows.
You will have a border of Seed st surrounding a center section of Stockinette st. You could cast on a smaller or larger amount of sts, depending on how large or small you want your blanket to be. Just make sure you use an ODD number of sts.