Another fan of Creative Grids. I started with a 6 x 24, easy to cut lengths of fabric, a 12 1/2 square, and a 6 x 12 1/2. I wouldn't buy a specialty ruler, until I had a need for it to make a specific pattern. Amazon also sells Creative Grids, if you can't find in your LQS.
I wish I had not bought so much stuff and never used it......that I had bought only when I was ready to use. sigh!!! would have so much more free space in sewing room.