How do I narrow photos down? Do I need both my photo stream and shared?

[iMore Question]

how do I narrow photos down? Do I need both my photo stream and shared?

For a while now, I've been getting error messages about not being able to back anything up on iPhone because of storage issues (I have used 23.5 GB and I have 3.5 GB available) I'm trying to delete unnecessary things from photos to documents. I haven't been able to back anything up on my phone for a month. Any suggestions on the best way to free up more space?