I didn't read Grog's post so she most likely covered this already but it really is 3 things...

practice, anticipation and spinning....

practice- the more you shift the more familiar it will become
anticipation- look ahead and shift just before reaching a climb allowing a continuous smooth cadence
spinning- it is HARD on your body to push big gears... when climbing shift into a gear that allows you to keep your cadence high... this will help conserve your energy and save your knees as well!

before you know it this will be second nature...