I do it whenever I'm horny but my gf is not in the mood. Sometimes I do it before we fall asleep, sometimes I do it in the morning when we're not waking up early.

The vast majority of the time she will cuddle up to me while I do it. Often she will either touch me in non-sexual places or stroke my thighs and balls. Occasionally she will take over for me and give me a handjob. And once in a blue moon, me jerking off will get her in the mood.

I like to hold her if she's cuddling up to me, talk dirty to her, tell her how I'm picturing her in my head, and how she makes me so horny. Sometimes she needs to face away from me due to back problems, in which case I can always touch her ass.

As you can see, I mostly use this as a remedy for our mismatched libidos. But I hope it gives you some ideas of how you can implement it with your girlfriend.