Adjusting your stem and handlebars can make the bike fit you a lot better if you haven't tried it yet. This tutorial is for the basic quill stem. As a side note the most standard size for them are 22.2mm (1in stems) at the base and the handlebar clamps are usually 26mm. French stems and stems off of old American bikes (Schwinns) are usually a bit smaller (22mm).
Quill stems can be adjusted up and down and the handlebars can pivot around the clamp. Generally, when the stem is mounted higher, it reduces the amount of reach that you have to do. This effectively makes the bike more comfortable and less aggressive for most people. When the handlebars are pivoted further up, this also reduces the reach distance.
Here’s a schematic of how it works. I know, its a masterpiece. When you tighten the clamp bolt it pulls the clamp up against the stem. The two pieces are cut in an angle so that they slide in opposing directions towards either side of the headtube wall when they’re pulled together. This wedging force keeps the stem in place! sooo simpo.
Get it to about this level. If you unscrew it too much the clamp underneath will fall off and you will have to take the whole stem out and flip the bike over to get it out.
At this point you want to knock the clamp piece out of its position so that it frees your stem. Use a piece of wood and a hammer so that you dont damage the face of the bolt. Give it a good whack so that the bolt goes down.
Once the bolt is down. Position yourself like so with your legs straddling the wheel. hold the wheel tight with your thighs and holding the handlebars, give em a good amount of torque. Some bikes might be harder as they’ve been sitting for awhile. Once it starts turning loose, wiggle it either up or down depending on how your want your stem to be. If you’re planning on putting the stem up higher there will be a Minimum insertion line on the stem. Don't let this line stick out of the headset for good measure.
Once you have it where you want it use the allen wrench and tighten it back up.
Get a good view from up top and make sure that the stem is aligned with the wheel before you completely tighten it down.
Now for the handlebar angle there’s a bolt on the bottom of the stem. Loosening this will allow you to rotate the handlebar around the clamp.
Putting it up will again make it less of a reach, but don't put it up this high, it’ll just look retarded.
Putting it low will make it a further reach, again don’t put it this far down, it looks retarded and you wont be able to use it correctly.