Here’s a graphic developed by César González. It breaks down how offensive sequences begin – after receiving serve, after a dig, from a free ball, or from a cover ball. It’s based on the women’s game. If you were looking at the men’s there might be a littler higher % from reception and cover, with fewer from defense. Maybe. I’d be interested to see the figures.
So what you’ve got here is a way to think broadly about how to allocate your training focus. It’s no coincidence that professional teams do A LOT of training working from serve receive.
You’ll of course want to take a look at figures for your own level of play. My feeling is that for a lot of teams the percentage of offensive plays in practice starting from free balls is way higher than what happens in game situations. The reverse is likely true for serve receive.
You may find this post’s figures interesting as well.