We weren't that smooth the first time
My first time being stroked by a girl was actually humorous. I was 15, she was 16 and we had dated most of my freshman year. She was very cute with blue eyes and large boobs for her age. The male teachers noticed, let me tell you. We went through the various stages of petting starting with breasts and leading up to me fingering her. One night she announced that she wanted to make me cum. No arguments from me!
We planned to do it one evening in her parents' living room. She started stroking me and had a towel handy. It felt so great, but took me a while because I was self conscious about her seeing my cum. Finally, I couldn't stand it and told her I was almost there so she could grab the towel. I closed my eyes as the first explosion hit. She jumped, said 'oh no', and let go of my dick. My first stream shot way over the towel, which surprised her so much she dropped it. When I opened my eyes she was trying to catch the remaining shots in her hands. When I was done, she ran to the bathroom with her hands cupped.
We tried again about a week later and it went much better. She really loved her hand jobs even after we started having full sex.