The important thing to remember when climbing hills is that speed has nothing to do with it...
effort is what is important. By that I mean you want to maintain an even amount of power and stress in your legs and on the pedals. As you approach the hill shift down once automatically whether you think you need to or not. As you are on the hill you need to make sure you are putting the same amount of force and effort to the pedals that you would if you were on the flats. As soon as it feels like you are going over the amount of effort it would take to maintain a constant cruising speed on level ground or if your legs/lungs/body begin to burn in any way shift down immediately and keep going until those unpleasant symptoms return or it feels as if it is taking more effort or pedal force to maintain climbing the hill, at which point shift down again.
Continue putting out the same amount of effort and shifting down until you reach the top of the hill where you may rest or continue riding, as you feel necessary. It is very important that you listen to your body, it will tell you if you are putting out too much power by burning muscles/lungs, racing heartbeat, feelings of fatigue, or a complete dropping off of your energy level. The second you begin to feel the slightest hint of any of these symptoms is when you shift down, not before and not after.
Also try not to rise up and stand on the pedals, remain seated on the saddle of the bike for as long as you can. Standing on the pedals allows for greater short burst acceleration at the cost of killing your endurance. The reason for this is simple, when seated the legs only have to worry about applying force to the pedals, when standing however they also must contend with supporting the weight of the body and doing so obviously takes more out of your legs than if you were to allow the saddle and your ass to take care of that end of things.
Trust me on this, using these techniques have allowed me to climb mild hills continuously for a mile at a time when I am under strict orders from my doctors to avoid hills and inclines of any kind and by all reason should not be able to even ride a bicycle under any circumstances (let alone with the growing proficiency that I do).
If you want to know more about my situation read my intro topic. Until then good luck and keep it shiny side up.
