Where to Put Your Feet
Begin by learning where to put your feet on the pedals. Most beginners try to place the pedal under the arch of their feet, which is inefficient and uncomfortable. If you've never used toe clips or clip-in pedals before, this is almost certainly what you've been doing. The proper placement is with the ball of your foot directly over the spindle so the power of your stroke transfers to the crank smoothly and naturally. Getting the foot into the proper position may require a minor adjustment.
Making the Adjustment
With clip-in pedals, the adjustment is to your shoes. Follow the manufacturer's instructions to shift the cleat to the right place for your foot.
With toe clips, all you need to do is make sure that the clip is the right length to guide your feet into proper pedal position. For comfort and to extend the life of your shoes, there should be a small gap between the front of the clip and the toe of your shoe. If necessary, exchange the clips that came with the bike for ones that fit correctly. If you can't get the right size, you can make a slightly too large one fit by taping a piece of foam inside its front end.
From the feet, adjustment moves to the saddle. If you think about the motion of your leg during each pedal stroke, you'll quickly understand why saddle height is so important. At the bottom of each stroke, your knee is almost straight, but at the top it's bent fairly sharply. The higher the seat, the less bend there is in the leg, and the less knee stress there is on the down stroke.
When you bought the bicycle, the shop should have helped you find approximately the right saddle position, but this is an adjustment where millimeters count, and it's going to take some fine-tuning to get it right. There is no consensus on ideal seat position. The only thing most experts seem to agree on is that many cyclists ride with their saddles too low. And within limits, too low is worse than too high.
You want to set your seat high, but not so high it hyperextends the knee at the bottom of the pedal stroke or robs you of power because your feet lose contact with the pedals.
Finding the Right Height
Sit normally on the bicycle with someone holding it upright to help you balance. Put your feet in the toe clips or clip-in pedals, and pedal backward until your foot reaches the bottom. Racers, who draw power from calves and ankles as well as thighs, will tend to have their toes pointing downward at this point. Recreational cyclists are more likely to have their feet closer to level. Regardless, your knee should be slightly bent. If it's locked, you're too high. Adjust the seat accordingly.
What matters is putting the foot in the same position you'll be using on the road. If that changes as you gain experience, you can always readjust your seat height.
Another approach is to take the bike out on the road or put it on an exercise stand. Pedal, while another cyclist watches you from behind. If your pelvis rocks back and forth, your seat is too high, forcing you to reach for the pedal at the bottom of each stroke. Lower it to the point slightly below the one at which you start to rock.
A third, time-tested approach is to pedal backward with your heels on the pedals, adjusting the seat until you find the maximum height at which your feet maintain easy contact with the pedals, all the way around.
These three approaches probably won't give you the same result. Try them all, and since too low is worse than too high, pick a height near the upper end of the resulting range. If you feel twinges of knee pain on your first excursions after a change in saddle height, adjust the seat by a couple of millimeters (probably upward), and see if they go away.
You might think that once you get your seat properly adjusted, you'll never need to change it. But that just isn't the case. Buying a new pair of shoes with a different sole thickness will require a change in seat height, as will purchasing a new saddle. And some days, the height you've always used just seems inexplicably wrong.
Making the Adjustment
Adjusting seat height is a 30-second job, faster if your bike, like some mountain bikes, has a quick-release lever on the seat post. Loosen the seat post (either with the quick release lever or an Allen nut at the top of the seat tube), pull the seat up or down as needed, and tighten it again. Work in small increments; for fine-tuning, one quarter of an inch is a big change. To keep from losing track of your starting point, mark it with tape or by lightly scratching the seat post.
Whatever you do, don't exceed the maximum safe-height line inscribed on the seat post. Look for this line the first time you adjust your saddle height so you're sure you know what to look for. If you need to go higher than that, get a longer seat post.
When adjusting saddle height, wear your cycling shoes, and if you're planning on buying a gel seat cover, mount it first. Otherwise, you'll have to adjust the saddle all over again.
Forward-and-Back Position of the Saddle
In addition to adjusting your saddle height, you can adjust its tilt and forward-and-back position.
This adjustment might have some impact on knee comfort, but more than anything else, it affects the power delivery of your pedal stroke.
The classic rule of thumb is that when the pedal is in its extreme forward position, a plumb line dropped from the point of the bone that protrudes just below your kneecap should go through the ball of your foot, bisecting the spindle of the pedal. Bike shops experienced with making this kind of adjustment actually have plumb lines they use for this purpose. If you decide to do it yourself, have a friend eyeball your knee/foot position as you sit stationary on the bicycle.
Making the adjustment
The saddle is clamped to the seat post by a pair of metal rails that are part of the saddle's frame. Loosen the bolt securing the clamp and slide the saddle to the desired position. Don't remove the nut completely or you might have trouble reinstalling it.
If the saddle won't go far enough forward or back, you might need to change the seat post. Clamp position varies from brand to brand.
Too much forward saddle tilt throws weight uncomfortably onto your hands, while too much backward tilt can cause groin discomfort. It's a trade-off you'll have to make for yourself.
Men should start with the saddle level or tilted slightly upward in front. Women may want to tilt it slightly downward, though a well-designed woman's saddle will reduce the need for doing so.
Making the adjustment
This is usually controlled by the same bolt that controls forward-and-back position. Because it comes under a lot of torque as you shift your weight in the saddle, this joint often uses a notched mechanism to keep it from slipping; you'll have to adjust your saddle by full notches rather than partial steps.
To adjust tilt, you shouldn't need to loosen the nut as much as you did to slide it on the rails. Adjusting the seat forward and back might accidentally disturb your tilt adjustment, but not vice versa — convenient, since tilt is the adjustment you're more likely to tinker with.
This is largely a matter of personal choice. For racing, the issue is one of aerodynamics; for recreational cycling it's one of lower-back comfort and getting the weight off your hands. An old rule of thumb is to start with the top of your handlebars an inch lower than the top of the saddle. I like to keep the handlebars higher, nearly even with the top of the saddle, sacrificing a little in wind resistance in exchange for comfort and an easier view down the road without craning my neck.
As with saddle height, don't exceed the maximum height line inscribed on the stem. Raising the handlebars higher than this risks breaking the stem, which could leave you cruising along with no way to steer.
Making the adjustment
The stem is held in place by a long expansion bolt inserted from the top. Tightening the bolt enlarges the diameter of the stem slightly, pressing it firmly against the inside of the head tube.
To change your handlebar height, loosen the stem bolt with an Allen wrench but don't remove the bolt completely. If it loosens a quarter of an inch or so, but the stem won't move, bang on top of the bolt with something hard to knock the expansion nut loose. Then slide the stem to the desired position.
Retighten the bolt firmly enough that the handlebars won't twist when you hit a bump, but not so tightly that the bar ends might impale you rather than twist in a crash. To test for proper tightness, stand in front of the bike holding the front wheel between your knees. The stem should rotate — grudgingly — to a hard twist. If you don't know how tight is tight enough, ask a bike mechanic to demonstrate.
The tilt of your handlebars affects how comfortable it is to reach the lower position on drop handlebars, and how much weight rests on your hands. It's not as important on upright handlebars, although it will affect the tilt of your extension levers.
Even for drop handlebars there are enough styles on the market that there's no simple rule of thumb for this adjustment. Most people, however, will probably want the handlebar ends pointing somewhere between level and aimed at the rear hub. Tilting them dramatically upward or turning the handlebars upside down, as a few people do, is dangerous because it puts the bar ends right where your stomach might hit them in a crash.
Making the adjustment
Loosen the bolt clamping the handlebars to the stem and rotate the bars as desired. When finished, make sure this bolt is tight. If it slips, you'll be lucky not to crash. Don't tighten it absurdly; I watched a mechanic do that once, shearing it and sending the broken end shooting across the room like a bullet. Do that on the road, and you'll be stranded.