I agree with quiltsRfun and stitch about 1/4 inch from the seam. By trial and error I found that the stitch size and straightness was effected by the number of layers of fabric, especially where blocks or points met, when I stitched too close.
I use a quilting foot and find the edge of the foot is a good guide. I also increase the stitch size.
You might also want to consider how much you want your stitches to show. When I first tried SITD I used a white top stitch thread - it looked terrible and emphasised every wobble! I now like to use a light grey or cream thread that blends in with the fabric. The result is you can see that the fabric is quilted but you can’t see the stitches as much. Sometimes, when grey or cream isn’t appropriate for the whole quilt, I quilt blocks individually in a colour that matches the block.