Walking uphill: pace, step length and breathing
Much of the difference between an easy climb and a miserable one comes from technique rather than fitness. Pace, step length and breathing can all be adjusted on the next hill.

How should you walk uphill without wearing yourself out? Slow down more than feels necessary at the start, shorten your steps, and choose a pace at which you could still speak in short sentences. Keep the rhythm steady, breathe through the nose and mouth as comfort requires, and stop for a moment when you need to rather than pushing until you are gasping. A hill is long, and the first few minutes set the terms for the rest of it.
Climbing feels like a fitness problem, and fitness certainly matters. But a good share of the difference between an easy climb and a miserable one comes from technique: how big the steps are, where the weight sits, and how evenly the effort is spread. These are things you can change on the next hill without getting any fitter.
Start slower than you want to
The most common mistake is setting off at your flat-ground speed. The first hundred metres feel fine, then the breathing climbs, the thighs start to burn, and you are forced to stop well before the top. Starting deliberately slowly is the cheapest fix there is. A pace that feels almost embarrassing at the bottom often turns out to be the one you can hold to the top.
A simple check is the talk test. If you can say a short sentence between breaths, you are probably in a sustainable range. If you can only manage a word or two, ease off. Heart rate, breathing and perceived effort all vary from person to person, so a number from someone else is not much use. What matters is that you can hold your own pace for the whole of the climb.
On a long ascent, the pace you want is a rhythm rather than a speed. Many walkers find it helps to count steps against the breath for a while, say two steps in and two out, and to let the count shift as the slope changes. That sort of regularity takes attention away from how far there is still to go.
Shorter steps, lower gears
On a steep slope, a long stride demands a big lift from the back leg and a big push from the front. Shorten the step and each lift is smaller, the knee does not have to rise so high, and the heel can stay close to the ground. A quicker, shorter step on a steep section is the walking equivalent of dropping down a gear on a bike.
Place the whole foot on the slope where you can, rather than only the toes. Landing on the toes loads the calf and Achilles tendon harder, and on steeper ground the heel can sit slightly lower than the toe without trouble. Where the path has natural steps, use them: a flat rock or tread of earth gives a level base, and stepping onto the middle of the foot, not its edge, spreads the load.
Lean from the ankles rather than the waist. A slight forward tilt keeps your weight over the feet on a slope; folding at the hips pushes the head forward and makes breathing harder. That is the same principle as in why weight transfer matters when you walk: one foot takes the weight fully, the other lets go, and the body moves smoothly across.
On a climb, the useful question is not how fast you can go but how evenly you can spread the effort, so that the last stretch costs about the same as the first.
Breathing without forcing it
No special breathing method makes a hill easy. Breathe in whatever way is comfortable, through the nose when the pace allows and the mouth when it does not. Trying to control the breath too tightly often makes it less natural, and a clenched jaw or hunched shoulders make it harder still.
What helps is posture and rhythm. Keep the chest open by letting the shoulders drop, and avoid hunching over the pack straps. If you find yourself holding your breath on a hard step, which is common, let it out in a long exhale and carry on. Slowing down by a few steps per minute will do more for your breathing than any technique.
If breathing becomes very laboured, you feel dizzy, or you have chest pain, stop and rest. These are not signs to push through. If they happen on ordinary climbs, or breathlessness is out of keeping with your usual fitness, it is sensible to speak to a doctor before your next walk.
Using your arms, poles and pack
Your arms can help. Letting them swing naturally, bent at the elbow, counters the rotation of the hips and keeps the movement fluid. On steeper pitches some walkers put their hands on their thighs for a few steps, which is a perfectly good way to share the effort with the upper body. Walking poles, set slightly shorter for the ascent, can take a share of the work and give a steady rhythm to follow.
A pack matters more on the way up than most people expect. Tightening the hip belt so the load sits on the hips rather than the shoulders helps, and a pack riding high and close to the back tends to feel steadier. If it swings or drags backwards, adjust the straps before the climb rather than halfway up it. There is more on this in how a backpack changes your balance.
Pacing a long climb
For climbs of an hour or more, think in stages. Pick a landmark, a stile, a cairn or a bend in the path, walk to it at your steady pace, and take a short pause if you need it. Pauses of thirty seconds to a minute, while you look at the view or take a drink, are often enough to bring breathing back down without letting the legs cool and stiffen.
Take a drink and a snack before you are hungry or thirsty, since the effort of a long ascent can mask both. If you are walking in a group, the pace should be set by the person who finds it hardest, not the one who is strongest. A group strung out up a hillside is not enjoying it.
Pay attention to how you feel at the top. If you arrive with your legs trembling and your breath ragged, the pace was too high or the step too long, and you now know for next time. If you arrive tired but steady, with something left, you probably got it about right. The ground will not change, but the way you meet it can.
Books worth reading: If you want somewhere to practise, Best Walks in the Lake District sets out fifty mountain days, and there are more on the Hiking Books shelf.