My first full-fledged crocheted garment was a jacket made of two giant granny squares, crocheted together into a 'T' formation. The two squares were seamed together to form the spine, the opposite edges left open as the front of the jacket. The sleeves and collar were crocheted off this form while working a sc edging round the whole shebang.
I wouldn't mind remaking it. Or even finding it so I could wear it on the cool days to come.
I think the most important thing to keep in mind when experimenting with granny squares is this:
Granny Squares can be...
squares
rectangles
diamonds
two triangles together