Catrin,

What really helped me with gearing was having a cadence meter. Currently, I have a target cadence when riding of 85rpm. I've noticed when riding if I get into my sorta auto-pilot pedaling mode, I can tell when to shift based on my cadence. When it starts to drop, I need an easier gear, as it goes up I need a harder gear.

I think once you start riding for longer periods, you'll start to discover a feel to both the gearing and your pedal stroke (I'm still struggling with efficient pedal strokes, based on feedback from the trainer in my cycling class).