I work to very simple plans because anything complicated troubles my mind. As follows:
1. I pretty much always start in amiddle-ish gear of the small chainring (only 2 on a road bike, as God decrees).
2. Once I'm up and pedalling, I like to pedal at around 95-100 rpm. So I cog up or down to get there.
3. Much over about 19-20 mph I might whop it onto the bigger chainring.
4. I prefer not to get the chain too crossed, so I avoid where possible running on big/biggest or small/smallest.
5. Getting back out of the big chainring is the funky one; I sometimes don't want to drop that far, so I do 'both thumbs together'.
6. For a short change of gradient, I don't bother changing and just pop up off the saddle.
7. For all the technical wizardry of indexed gears and ergo levers, I often just change to any gear that's 'a bit higher' or 'a bit lower'. It's not very scientific.
8. As long as I'm moving at a decent pace and my knees are moving at a good speed, I figure the gear must be about OK.
9. In my whole life I don't suppose I've gone all the way up or all the way down a set of bicycle gears. I prefer just to go 'click... whirrr... that'll do.'