Most of my puzzles are designed with a little more than 2 pieces per square inch. Thus a 15 3/4 x 19 3/4 puzzle has 311 square inches and about 700 pieces. I try to make the longest dimension of each piece longer than one inch and shorter than two.
I use three puzzle styles shown below. The one on the left is the one I started with and I still use it, most recently for “Rooster”. The sample shown is from the lower left corner because that is where my signature piece, the cat by the French cartoonist Dubout, is. The second style in the center uses more but smaller arcs. I used that style for “Gracie”. The style at right is different. It is based on a grid of equilateral triangles, not squares. Therefore three lines cross each other at a point rather than two. Of course the grids are references and get put aside whenever a figure piece gets in the way which is most of the time.