I usually attach streamers with a bit of masking tape. That secures it adequately while not pulling up paint on removal.
Any conveniently located surface will do, even the control surfces themselves. just make sure it can't get caught in the control linkages or the prop and that you maintain some sort of balance (If you put one on the left wing tip put one on the right as well for example)
Also I usually cut the streamer in half while it's still rolled up, so it's only half the width. A hack saw works fine for this, though you need to be careful.
I have a 3d-printed tool that makes it safer and easier, if I find the file for it I'll post it in the resource section at some point.
Start with a short piece of streamer, some 2-3 feet is enough, then lengthen it when you become more comfortable with it.
Be aware that the streamer induces quite a bit of drag so your motor might run hotter and your battery life will be shorter.