Some thoughts, not necessarily coherent, nor complete. I’m guessing you mean a workshop as something where a group of people work and play with an idea in mind and a goal of learning something by doing. And I expect you’re facilitating it. So here’s what I do when I’m doing that.
I plan using a circular timeline – it helps me judge rhythms and see connections, and I find it helps me feel how something will work in context of neighbouring activities and the overall flow and energy of the full workshop.
I tend to look for some sort of narrative – to learn means being changed, and a journey helps people to make sense of that change. Sometimes the narrative is a story, sometimes a linked set of ideas. I try to I change the space, or to encourage people to physically move, so as to stick flags in the timelines of people’s memories. Make flipchart pictures as you go, stick them the on the walls, get people to walk up and interact with them.
I tend to to switch formats 3-4 times an hour. My usual formats include individual exercises, whole-group discussions, small-group activities and lecture-style bits. Everyone needs a break, too. If you need to hit hard timings, have a few short bits that are done in 5 minutes, and know how to reduce some of the longer activities by 5-10 minutes, too.
I try to think through my workshop, in sequence, from various perspectives; my own, various participants, various resources. Doing this helps me uncover points where the narrative breaks down, things I need to supply to the participants or to prepare beforehand, stuff that will need redundancy or backup. I try to run new bits for fun (but for real) before I get to put the whole thing together.