I found this gem of a tip from Melissa Leapman on Vogue Knitting International:
“I like the look (and the speed!) of solid double crochet stitches, but I hate the little holes that often appear next to the turning chains. Here’s how to use “linked dc stitches” to prevent them: Immediately following the turning chain, insert your crochet hook into the second chain of the turning chain just made, then yarn over hook and draw the loop through the chain—two loops will be on your hook. Then, insert the hook into the next stitch the regular way (that is, into the second stitch of the row), yarn over hook and pull up a loop—three loops will be on your hook. To complete the double crochet stitch, [yarn over the hook and draw the loop through two loops on your hook] twice. Easy!”
I love this and will definitely be using it on my next crochet project.