I'd gladly describe to you how I decided to make fun out of my sessions back in June 2012 when I got tired of not being allowed to make responses for the tupplah. Butt, that fun was based on parroting, which in turn was based on going off on the wildest of tangents and making up oftentimes very cheerful responses for her that fit her personality, and I happened to know her personality well.
You? You barely know how you want Miriam, you can't be arsed to deeply explore how she'd think and thereby put yourself in her shoes, you find meditation and anything that involves sitting down and focusing mind-numbingly boring, and your repeated failed attempts at getting anything productive out of the narrative approach (which I tend to not recommend) have led you to form a rather negative mindset about tuppers in general at this point. If I didn't know any better, you want a fresh Tupla that completely acts on its own and didn't require any forethought served on a silver platter. You come off to me as a person that only has little imagination, especially because you can't visualise very well, so a crap tip like "Just, like, relax and let your imagination go and figure out how it wants to make the tupper on its own." is something I wouldn't want to give to you. But I know someone else who probably would under some circumstances. But enough about him.
A combination of a lack of imagination, dedication, focus, empathy, introspection, and all those other goodies is what has brought you to where you currently are. I'm used to blatantly advertising my method as being the easiest to pick up for those that failed with the narrative method, but in your case, even my suggestions probably aren't worth the trouble when you're at the level of not being able to make up a personality and thoughtful responses for it, or use your imagination for something more sophisticated than thinking "I want an imaginary girlfriend that's chill and fun... and... yeah."
Good game, guys. Had a good run. Was fun, y'all.
...
Well, anyway, in case you're still up for it, then you can always go ahead and make one of them extensive character sheets, building up her personality bit-by-bit by picking out a metric shittonne of traits and thereby know a lot more about her. Using those traits, you can then go ahead and use that as fuel for imagining how she would react in certain situations based on her traits, and sort of explore her personality like that, using the method I described in that earlier post; what would she be thinking in the situation, why would she do what she would do? You don't know? Ah, but you have a trait! That should tell you something. Seriously, it's not that hard. It's just like if you're thinking to yourself what you would do in a situation. Except it's not you but someone else, and in a different situation.
Here are some sample personality traits to get you started, shamelessly ripped off from Dane. Optionally, and preferably, you should write some short sentences for as many traits as possible about how the trait in question exactly influences and defines her, and not just "She's chill... yep, that's it."
Energetic, laid back, brave, meek, sarcastic, creative, dull, forgetful, retentive, hardworking, lazy, optimistic, realist, cynical, opportunist, social, introverted, easily amused, often bored, dependable, open minded, sceptical, articulate, simple, strong-willed, confident, friendly, protective, loyal, honest, passionate, resourceful, independent, outgoing, immature, mature, intelligent, comical, logical, consistent, a leader, motivated, not regretful, not gullible, helpful, patient, empathetic, introspective, talkative, thoughtful, mischievous, fierce, hardy, outdoorsy, adaptable, content, reasonable, coordinated, charming, perceptive, observant, trustworthy, quiet, secretive, rebellious, witty, rambunctious, uplifting, faithful, atheist, critical, materialistic, silly, inclusive, agreeable, blunt, sane, accepting, selfless, stoic, meticulous, mean-spirited, snide, handy, motivated.
And if you can't think up situations to imagine her in, just think back on what you've done recently in your life; what would she have done if she were you? Or, perhaps, what would she have done in some of those roleplays? That's at least something if you can't think up anything. There you go. Another tl;dr post.