Absolutely IMHO the right strategy, learn by doing. I would even start by saying at the outset that it will not make sense to them or seem useful at first (and maybe won’t at all) but one has to form their own opinion based on experience. I made up something called the “Twitter LifeCycle” that was pretty much my path in 2007- my first reaction was “this is the dumbest thing I have ever seen”
I might add something related to having them learn to follow a hash tag. Maybe you can ask them as a group to come up with their own one (after searching to make sure it is not in use), and see how much activity they can generate around this.
For getting started, I would also have them make sure they select an icon for their account, and fill in their profile.
It’s useful for them to (maybe) when choosing someone to follow, to sift through their tweets and think about “is this person worth following?” I even suggest looking at other people in a stream a person regularly corresponds with. This is a way of doing a rhizomish thing 😉
The important effect is to have them see what happens when people they do not know respond or interact. This is where you can use your own twitter network to invite people to respond to your students tweets.
The photo exercise is great; I like the closeup where you have to guess what it is, as it invites response. Another activity I have seen a colleague do in teaching ds106 is ask students to create an interesting photo of a shadow. It’s open ended enough to interpret, it gets them looking for interesting shapes and light, but also is a less invasive way of posting photos of themselves without it being of their faces.