Lisa G - to reduce the amount of fabric that shows between stitches, you'll need to up the number of strands of thread you are using. On 14 count, most people use either 2 or 3 - do a few test stitches with both and see what coverage you like better. 18 ct will use 2 strands, 22 ct - use 1 or 2 - again see what you like better. 28 ct will use 1 strand if you are only going over one square, but 2 or 3 if you are going over 2 squares. Here is a link that shows what the coverages will look like on various sizes of aida cloth.http://www.better-cross-stitch-patterns.com/floss-coverage.html
Hope that helps a little. Happy Stitching.