I had the same question, this article is in the article section of this forum under hills/climbing tips under the popular articles
STAY SEATED AS MUCH AS POSSIBLE
Although you develop more power while standing (taking advantage of your upper body weight), you also use 10 to 12% more energy as you work your arm and back muscles. So climbing while seated is more efficient. On short climbs, the length of a football field or less, it makes little difference. But on longer climbs, stay in the saddle and spin at 80 - 85 RPM. This is particularly so if you are heavier as standing puts just that much more weight on your leg muscles, while sitting uses the seat to help take the extra upper body weight off your legs. Staying in the saddle will:
burn less energy - heart rate is approximately 8% lower for any set speed
use your bigger gluteal (butt) and hip muscles to your advantage
So whenever possible, stay seated on that hill.
SIT BACK ON THE SADDLE
When you slide back on your seat, you gain a leverage advantage on the pedals. The only time you would want to slide forward is for a short sprint on a small rise.
UPPER BODY STILL AND CHEST OPEN
Keep your upper body quiet - the bike should rock under you (try pulling up on the handlebar opposite of the leg on a down stroke). Too much movement wastes energy. And your shoulders should be back and "open". If not, you are constricting your chest and cannot breathe efficiently.
WHEN YOU MUST STAND
If you must stand, remember to power into BOTH the down and up strokes - 12 to 5 o'clock on the down stroke and 7 to 10 o'clock on the upstroke. This will help to maintain a smooth stroke and your momentum. Don't lean too far forward. If the nose of your saddle is brushing the back of your thighs, you are just right. Farther forward and you will lose power. Let the bike move fluidly under you. Don’t force it. And remember to shift up a gear or two just before you stand to take advantage of the extra power you gain from standing (but which you can’t maintain for any length of time).
FIND YOUR SPEED AND RHYTHM
Climbing should always be done in your comfort zone. Ride at your own pace - Know your limits and listen to your body. If you become anaerobic, you won't recover, so let faster riders go. It's a common mistake: Trying to keep up with better climbers on the lower slopes, then reaching your limits and losing big hunks of time. Take it a bit easier and you have a much better chance of catching them later. You don’t want to over exert and go anaerobic.
Gear down before the hill. The goal is to avoid producing large quantities of lactic acid and then pedaling through the pain. You want a sustainable rhythm. Try to keep your cadence above 70 -- any slower puts excess stress on your knees. The optimum spin rates for efficient pedaling are somewhere between 70 and 80. One rider reported that he actually went faster as he increased his cadence in a lower gear. For example, he would maintain 6.5 mph at 50 rpm in one gear and then, as he geared down, he found he maintained 8 mph at 70 rpm without a perceived increase in effort.
Try to find the cadence that would let you "climb all day". You are pushing too hard if you:
- Can't keep a smooth pedal stroke
- Are panting or breathing irregularly
Ride your own pace. The energy you save may help you catch someone who started too fast near the summit.
BREATHING
If you start to breathe irregularly, take a deep breath and hold it for a few pedal strokes. Try synchronizing your breathing with your pedal stroke - start by taking a breath every time one foot (your right one for example) reaches the bottom of a stroke. Then try 1 1/2, and finally every two strokes. You will actually deliver more oxygen to your system with a controlled rate than an irregular panting or gasping one.
HAND POSITION
Comfort overrides these comments, but for seated climbing, most riders prefer to keep their hands on top of the bars, perhaps 2 or 3 inches from the center stem. And remember to drop your elbows and relax your upper body.
For out of the saddle climbing or aggressive climbs (where you are accelerating or attacking on the saddle) put your thumbs on the hoods and rest one or two fingers on the levers or wrapped around underneath. And when you get to that descent, most riders will go to the drops (keeping your wrists straight) for the aerodynamic advantages although others prefer the hoods for the feeling of control. But not the top of the bars as your hands will be too far from the brakes.