The below discussion is for counted embroidery. The two below links discuss purchasing fabric. If you are new to purchasing embroidery fabric or new to setting up an embroidery project I suggest you read both of these blog pages.
Purchasing fabric, Hardanger
Purchasing fabric, Bargello

Once you are set up to work you need to decide where to start the first stitch.
Viewing the above photos. The leftmost design (blue fabric) is the hardanger design that I am currently working on. I started in the center of a side as that was the easiest way to determine that my buttonhole worked edge would be 1-2 inches in from the fabric edge.
My first goal working this design was to establish the outline structure (the entwined pomegranate pattern) then come back through and stitch each of the inner areas.
For my first stitch, I started in the lower left corner then followed the 4:2 pattern of the outline structure’s graphed chart for the blue stitch lines. When finished with the blue stitch lines I came back and did the red stitch lines.
To determine how far in: If you decided to have 3 inches of unused fabric around your worked design you measure in 3 inches and up 3 inches from the fabric’s edge then bring your stitching thread through and begin to stitch.