What batting are you using? The higher loft the batting, the more difficult it is to quilt. Also, cotton batting is easier to use than polyester because cotton batting "sticks" better to the fabric. A widely available, easy cotton batting to use is Warm n Natural. It allows quilting to be far apart also.
If you are doing straight-line quilting, use a walking foot. This helps keep the layers from shifting on you as you quilt.
For me, spray basting is the best way to keep the sandwich stable as you quilt. It is fast, too. 505 is the best, but other brands in quilt stores are okay too. Just be sure to spray baste in a well-ventilated area, and put a large sheet underneath to catch overspray (toss in washer afterwards). In addition to spray basting, to be sure the quilt edges don't start wavering, pin along the edges every 4 to 6 inches. Use the "search" function at the top of the web page to find threads with detailed explanations of how to spray baste a quilt.
On your design, if you are doing stitch-in-the-ditch, I would do the center line first from top to bottom, then the center line from side to side. (I would work from one edge to the other so there are no thread ends to bury.) Work out from the center one line at a time, alternating top/bottom and side/side directions.