I volunteered in our DS school for five years, one morning a week, supporting Yr1 / Yr2 reading at first. School then asked me to hear readers in a couple of other classes, to 'push' slower readers, and also in Yr6 to encourage expression and comprehension for children who were about to transfer to secondary.
At the start it was made clear how to support reading effectively, and the school also ran some evening sessions for parents (not just volunteers) on reading with your child at home, and on early Numeracy concepts; the staff did it very well, acting out different scenarios of parent/child interaction, which were informative but also entertaining.
As I gained confidence, I went on to do a Friday afternoon practical gardening session with Yr6, and also ran an after-school Keyboard club for Yr6 children who had their own keyboards, encouraging simple improvisation and making up their own tunes. (Children can be afraid to 'have a go' at things like that, fearing that it needs to be 'correct' - which, of course, it doesn't.)
I then gained a post as TA in an Infant school, and was there for ten years, followed by two years in a tough comprehensive.
When I reached retirement age, I resumed voluntary work in different schools. One of my earliest 'readers' turned up again, seventeen years later, when she was on her final year of Teacher Training! Our roles were reversed, as SHE needed to direct ME in the classroom.
So, if you have any particular skills - sport, arts, music, ICT, dance, drama - schools often value support in things like that. As a TA I had many sessions of formal training, and at the Infant school our number of TAs rose from three to twenty during the ten years I was there.