Learning progress 
The time it will take before you can ride a unicycle varies greatly. Some (although few) learn it instantly as they step on the unicycle, while for others it may take months. The most important thing to keep in mind is that anyone can learn, just don't give up.
If you are interested in the correlation between time it takes to learn how to ride a unicycle and age, have a look at http://www.xs4all.nl/~klaasbil/agelearn_short.htm
It helps your inspiration to watch other unicyclists ride. If you do not have a friend who can show you, look at the links to the galleries below!
10 steps to Unicycling 
Contrary to popular belief there is nothing that I can tell you that will make you instantly be able to ride a unicycle. People always say "How do you do it?" like there's some magical thing I can tell you that'll make you be able to ride instantly. There isn't. However, there are things that can help you learn to ride. Before you try some of these tips, it may help to have a friend on either side of you for your first couple attempts. This will give you a chance to "understand" the unicycle.
- Find a handrail that's a comfortable height.
- The easiest place to learn to ride is on smooth concrete or asphalt. Grass is too bumpy.
- Get used to simply sitting on the unicycle whilst holding onto the rail.
- Start riding forwards whilst holding onto the rail. (2 hands on the rail to start with and then progress to one)
- Eventually, when you are comfortable holding onto the rail and riding, let go.
- Get as far as you can and repeat.
- Keep your weight mainly on the seat. This stops you from wobbling side to side as much.
- Pedal evenly.
- Look forward.
- Wave your arms if you need to. You can't look like more of an idiot than you already do.
*Note on safety: Wear as many pads as you can, and try make sure you land on your feet, don't worry about catching the unicycle. Dirty or broken parts are easy to fix, broken bones aren't.
Key points and tips 
Biking is much easier than unicycling to learn because on a bicycle, you only have to control your balance to the left and right. Also, on a bicycle, your wheels automatically stay under your center of gravity when you are moving forward. However, on a unicycle, you don't have that luxury. You have to balance in the forward and backward directions, as well as to the sides. Since side balancing is mostly taken care of by precession, forward-backward balance will be your key concern, at least at first.
To accomplish this, your weight must be farther forward than will feel normal for most people. You have to keep the unicycle under you, rather than you on top of it. So, if you lean forward and then pedal forward, the unicycle should be under you. This takes a while to get used to for most people, as the four-directional (forward, backward, left, right) balance is tricky. Don't fear! It will come with practice. Practice is the most important thing in your learning process.
If you have a specific problem that is not covered here, search the forums at Unicyclist.com and if you cannot find an answer, ask a question.
Why did I fall off? 
Basically, when you fall off you can always find the reason. This can help you correct the problem and improve. If you fall off the front you are either not pedaling enough (likely) or leaning too far forward (not as likely). If you fall off the back, you are either leaning too far back (likely) or pedaling too fast (less likely). If you fall off the side, you are probably not going anywhere. When you are learning, you always want to keep a forward momentum!
Saddle soreness 
It is normal to experience some discomfort when you start unicycling. This normally goes away as you learn to move some of the weight from the saddle to the pedals. Try to keep 1/3 of the weight on the pedals. Contrary to common belief, this is not only a problem for men!
Not all saddles are equal, especially when it comes to comfort. Many saddles, including Miyata and Viscount, have very little padding. If you have a saddle like this, you should consider either performing an airseat conversion on your saddle or replacing it with something with more padding such as Kris Holm or Koxx. The KH Fusion Freeride saddle seems to be generally accepted as the most comfortable unmodified saddle currently available.
Some things to try in order of importance
- Wear bike shorts with padding
- Change the angle of the saddle so that it's higher in the front
- Try a cycling lubricant like Chamois Butt'r
- Practice riding standing up with all of your weight on the pedals, and stand up a little while for every minute or so as you ride
- Lower the seat post by a few cm
I drift! 
It is common that you drift slightly to the left or to right in the beginning. It usually goes away as you get better at unicycling. Things you may try include but are not limited to
- Check that the saddle is straight
- Check your posture, you should sit straight
- The road may be slanted. Most roads have a crown in the center and a slight slope to the shoulder.
If you want to actively attempt to correct your drift, there are several ways to practice. These methods below may quickly show you whether it's harder for you to turn or balance at a particular angle.
- Ride in figure eights, try to keep all of the turning smooth and incremental
- Keep your back straight, and try to ride with your hands at your sides or behind your back
- Ride in lots of circles with decreasing diameter in the opposite direction of your drift
- Try riding with one shoulder or the other forward, you can encourage this by having one hand reaching across your body in front, and the other hand reaching across your body in back
Seat height 
When you begin unicycling it helps to have the seat high in order to transfer most of your weight to the saddle. The seat should be in a position where you can just barely reach down to the pedals with your heel when the pedal is down.
Free mounting is easier with a lower seat. For muni and trials you may want your seat a little or even a lot lower. When you start learning hopping, lower the seat by an inch or so. Then if that feels good, you could stay with that or try it even lower. The ideal height depends on the person and their style of riding.
When you learn seat out hopping having the seat too low may be uncomfortable and even put unnecessary stress on your shoulders, back, and arm.
Lowering the saddle may also help with saddle soreness.
Good Luck! 
Good luck with learning, don't give up! It will come with time and lots of practice!