its a bit tricky making a square from center outward..
garter stitch works best.
this is because knit (generic term here knit) stitches aren't square.
in garter stitch, ON AVERAGE, 1 stitch = 2rows (a 1:2 ratio)
in stocking knit, ON AVERAGE 3 stitches =4 rows (a 3:4 ratio)
some slip stitch patterns, and some times color work, like fair isle, even if it appears to be be all stocking knit (linen stitch say) will also have a 1:2 ratio.
Mitered squares (which aren't worked from center) can be square because you start with X stitches, decrease 2 every row, and so retain a stitch row ratio. but proper squares, need 4 increases (or better yet 8 increases to be square. and this makes it hard to keep an even row/stitch count ratio.
over on the BAKG web site, there is a free pattern for a set of interlocking mitered squares
(look under special/members projects, BAKG quilt.. it's about 3 pages to work your way in!)
the BAKG quilt 'square' is made from 2 squares knit from out side in(start wtih 25, end with 1 stitch in 12 rows) that are paired with 2 mitered squares that are made by picking up stitches along the edges of previously knit mitered squares, and knitting to outside corner.
i have seen several books on mitered squares, but i haven't ever seen a simple pattern for a knit from center out square.
(you can cast on 4, k1, m1, (4 times)
then k2, M1, (4 times)
then K3, M1, (4times)
followed by P4, M1 (4 times)
P5,M1, (4 times)
P6, M1 (4 times)
and continue in that pattern (each round, increase 4 times, in same spot, and alternate between 3 rows of stocking knit, and 3 rows of reverse stocking knit.)
but the square won't be a proper square! it will be a squarish spiral!
The world is waiting for you to figure out the right ratio of stitches/increases and rows to get a perfect square..