Everyone has their personal preference where to start on a project. I always start in the upper left area. Find the center of your material and the center of your pattern. Count up the number of rows to the top and then the number of squares to the left and that is where I would start.

I always start my projects in the center. Usually the patterns have the center marked so you know where to begin. It is just individual preference.

I, too, try to start in the center if at all possible. This way you are assured that you don't run out of fabric. It doesn't matter what shape your pattern has, start at the center and all will turn out well. I don't know what your skill level is but as you become more advanced you'll be able to just look at your fabric and gauge where to start. Good luck.

Did you buy fabric 3" larger than the design per side for mounting? Then you can go to the top center & place your stitch 3" down. Or, 2" down, if you only ordered 4" extra cloth.

Cross stitch is relational, so all stitches are related to your first one.

I often mark top/bottom,& sides centers with a water eraseable pen, so I have a visual of the design on the fabric.

Almost all the time I start my projects in the middle when the arrows help provide you where the center is. I'm more comfortable starting in the middle.
I have done a couple of projects in the upper left corner, AFTER I have measured down 3 inches and inward 3 inches and marked the fabric as to where that very first stitch should go. It still makes me nervous, (even after measuring it a couple times) to start in the upper left corner though. Both projects that I started this way I made sure I cross-stitched a couple rows of the whole pattern completely across to the upper right-hand corner to make sure the pattern fit on the fabric.