Length of normal shower: 8 minutes
Order of operations: Shampoo, Conditioner/shave with conditioner in, Wash body
Shorter shower: 5 minutes
Shortest shower: 3 minutes
For me, the quickest showers are the ones when I don't shave or wash my hair. I don't wash my hair every day, and usually shave every other day. So, cutting those two pieces out of the shower cuts down on the time quite a bit! Sometimes I will shave separately from the shower, and I feel that this saves a lot of water. It's hard to get into the habit of shaving separately, but it's certainly not impossible! But realistically, not every shower can be without a hair wash!
To make hair-washing faster I can open the shampoo and conditioner bottles before turning the water on so that they're ready to go. I can use a little less of each so that I have less soap to wash out of my hair. And, I can wash my body while I'm rinsing my hair.
But, I think the best piece of advice is to be consciencious of being fast in the shower. I am notorious for soaking in the hot water (in the winter, especially). If I put some pep in my step I am able to speed through my shower routine in nearly 1/2 the time it takes me when I'm not thinking about it.