It's always nice when we find some simple tip that will make our lives easier. One issue when working in overlay mosaic crochet is the loop pulling up as you work your double crochet stitch into the front loop two rows below. This ends up creating a gap that you don't necessarily want. The good news is there's a very simple way to avoid this.
When working your double crochet into the front loop of the stitch two rows below gently hold on to the bottom of the double crochet stitch with your thumb as you work it. This will keep the loop anchored in place so it doesn't pull up as you work.