It seems like all the bike books I read love to stick in quotes from Chris Carmichael wherein he states that a cyclist climbing a hill should be like a carpet unrolling, getting progressively faster towards the top. Carmichael also suggests starting in a lower gear than needed so you'll have energy to upshift as you near the top.

It was drivel like that that made me read less and ride more.

Personally, the best tip I have is this. I shift up as I stand up since it's easier to pedal a bigger gear while standing. Right before I return to the saddle, panting, red faced, with smoke pouring out of my HRM, I downshift.

Lou