It... depends. There's no quick answer because it depends on whether we're preparing for competition vs. trying to shore up fundamental skills, and also what we're preparing for competition in (AKC Rally, WCRL Rally, or competition obedience -- each one is different enough that I try to spend at least a couple of days prepping for whatever venue we're doing that weekend).
On top of that we had a pretty disastrous trial yesterday so right now I'm feeling like I don't know anything about anything.
But in general, yesterday excluded, I would say that I have a pretty clear sense of what we need to work on (currently defined as "anything we don't have competition-ready," meaning that either (a) it's not ready for competition at all; (b) I thought
it was ready but Pongu blew the exercise more than once at an actual trial so clearly I was mistaken; or (c) we're not actually blowing the exercise routinely but we are
regularly losing points on it), and whether the problem lies in the learning of the exercise (a and sometimes c above) or proofing (b and sometimes c).
Most of my training sessions are structured so that we work on new stuff first, while Pongu is freshest, and then go into proofing work after we've done X numbers of reps on the new stuff. I'm working on a BUNCH of different stuff now because we have infinity things that need improvement, so it's a constant rebalancing act.
I'm also working on thinning reinforcement rates for treats/praise and increasing the value of personal (non-toy) play while simultaneously trying to teach, proof, and build value into the exercises themselves, which also affects the order in which I ask for exercises. This means that I intersperse exercises Pongu really likes with other ones he doesn't like as much, and easy ones with hard ones. It also means that I put in play breaks strategically, with an eye toward increasing the value of the exercises he doesn't like so much. So... it's a lot of stuff going on at once.
What you're asking is a really good question. It's just hard to answer because there's SO MUCH that goes into it, and much of it depends on how you train, what your goals are, and what your relationship is with your dog. Also, a lot of this is stuff that I don't consciously think about anymore, so it's hard for me to sit down and try to puzzle it through. But it's a very interesting topic!