I would start with the rope framing first. Choose your size, shape, where you want to put it... etc. before gluing it down. My backing had a perfect indent, allowing for an easy square border.
Start at a beginning point and work your way out... gluing small sections at a time, so the hot glue doesn't dry before you get the twine down.
Second, you can either do the sand, or the corks. I found the corks stuck better straight to the backing frame. Up to you.
Arrange your corks first, before gluing.... in the pattern you would like to use. I used a standard 2x2 brick like, laying pattern. Once you have them laid out the way you like... hot glue one at a time, picking up in place, and gluing back to your design. This will ensure it stays exactly where you placed it.
The sand was the most time consuming part for me. Using the wood glue... I would paint a small section of glue where I wanted the sand to be. Sprinkling sand on the section of glue... and pressing the sand into the glue with my fingers.
I'm a bit of a perfectionist... so even after the whole section was covered in sand... I would turn the frame up on it's side, and knock it a couple times to see if any sand would move around. Then I would follow with a second coat. Repeat this until you are happy with the results.
Last but not least... place your beach decor. Small amounts of hot glue are probably needed, depending on how heavy the shells/starfish are. I didn't want to damage the starfish too much, or want anyone to see the glue, so I used a small amount.