I'm a big fan of squares with a variety of stitches/patterns provided they don't get too complicated, this is one based on a central flower:
Chain 5, make a ring with a slip stitch.
Chain 5, * 3 treble crochets, 2 chains, repeat 3 times, 2 treble crochets, join with a slip stitch round initial 5 chains.
Chain 3, 8 treble crochets in first corner space, 9 treble crochets in each of remaining 3 corner spaces, join with a slip stitch in third of the chains.
Slip stitch in next two treble crochets, chain 3, treble crochet in 5th treble from previous round, chain 3, slip stitch in final 2 trebles, double crochet in central space, repeat on each corner, join with a slip stitch.
2 chains, double crochet in each stitch round to corner, double crochet, 2 chains, double crochet in the treble from previous round, repeat on each edge, join with a slip stitch.
4 chains, miss one double crochet, treble crochet, *1 chain, miss one double crochet, treble crochet repeat from *, at corners do 2 treble crochets 3 chains, two treble crochets then continue with previous pattern.
I then did two rounds of double crochets to finish off - making it the required size.
Hope this makes sense, it's more complicated than I thought!