- Choosing a place that is looking for my skills, and incidentally seems like a good cause, vs.
- Choosing a place with a cause I care about, that might or might not particularly need my skills.
I find the second one works better, although it might be possible to have a bad enough fit to try something else. If you have a pre-existing connection to an organization, possibly have made donations, and you show up and ask what you can do, and then you prove that you don't mind doing simple tasks, you will likely graduate into technical stuff if that's what you want.
My impression is a lot of non-profits have a great need for technical help that their usual interns, volunteers and employees can't provide, but if you don't connect with them in the right way, it won't work out.