Learn-to-knit scarf

This is the first thing I ever knitted and is the pattern I recommend for a first project. The idea is to learn and practice the basic stitches until you gain the necessary confidence to go along and work in whatever else you want to do. The nice thing is that you'll actually be able to keep and wear the absolute first thing you've ever knitted. I know I do.

You'll learn the knit stitch first. Once you get the hang of it, you'll start learning the purl stitch and keep on practising the knit stitch so you won't loose what you've learned. Once you've got the hang of both, you'll learn and practice to switch between the two. In practice this means that you start by knitting in garter stitch, change to stockinette/stocking stitch, and then seed stitch.

I created the pattern myself as I went along learning the basic stitches. Basically I cast-on a bunch of stitches and started to practice the knit stitch until I got bored. Then I decided to learn the purl stitch, but it took me so much time to get it right that at the end of the first row, I'd already forgotten how to knit. So I decided to go back and do the next row in knit stitch. I went along alternating the two stitches every row in order to practice both. Of course I was pleased with the nice stockinette I got as a result. Then I decided to learn how to switch between them. Oh my was that a bad idea that turn out to be a brilliant one.

The seed stitch (and of course you can say the same about 1x1 rib) is the hardest thing to learn in my experience. But it is very important to learn it from as early as possible. Because if you, like me, are having problems with it, it is because your technique of knitting the basic stitches is bad and the sooner you correct it the better. Otherwise you'll get used to knitting or purling in a certain way and it will be much more difficult to correct it later.

The pattern

I'm not going to bother with an exact and standard pattern. This is a very simple project and you're a beginner so I'll give the best and most clear instructions I can. Check this post in order to learn the basics: cast-on, knit stitch, and purl stitch, as you go along, or learn it any other way you find better.

1. Choose your yarn and needles. Check this post for some advice on this subject (you can see from the photograph above I've learned the hard way the importance of choosing the right yarn).
2. Decide what approximate width you want your scarf to be, let's call this w. A scarf does not need to have an exact size, like other clothes, and unless you want to do a gauge swatch, which I don't think is necessary at this point, step 3 will result in a width which is only a crude approximation of the desired width. If you prefer a more exact measure, go along and do a swatch.
3. Check the label on your yarn. It should say something like n stitches/l inches or cm. This is only a predicted gauge for this yarn and when you knit you'll probably get a different result but don't worry about it. Now here is the easiest arithmetic you've ever had to do: w*n/l = N number of stitches to cast-on. Most beginners tend to knit very tight, so go along and add some stitches to N, maybe 10% will do. It is impossible to predict really, but just do it for now and then we'll see. If N is odd, add one. It's better to have an even numbers of stitches to simplify the seed stitch in step 7.
4. Go on and cast-on N stitches.
5. Start by learning the knit stitch. Check the videos, and go along and practice for some rows. Let's say 10 rows. You've just finished a band of garter stitch.
6. Are you already reasonably confident with your knit stitch and bored of it? Start learning the purl stitch. Do 1 row of purl and 1 row of knit alternating between them until you've done 10 rows again (or as many rows as you've done in step 5). You've got a band of stockinette stitch.
7. By now you should be fairly confident with both stitches. It is time to learn to alternate between the two. Knit 10 rows of knit one-purl one. Now you should have a band of seed stitch, unless N is odd, in which case you'll have rib stitch. If you have made some mistake and N is odd, you can still get seed stitch: alternate between rows where the first stitch is a knit and rows where the first stitch is a purl. It is a bit harder, you must keep track of what you did in the previous row, but it can be done.
8. Repeat the stockinette rows.
9. Repeat steps 5 to 8 until the scarf is the length you want, but do not end with a stockinette band. Cast-off. 
10. Stockinette stitch tends to curl (this is why we don't want to end with stockinette), but the bands of garter and seed help it stay flat. You should consider blocking your scarf. It'll stop curling if you do, at least mine did. Enjoy!

At any point, if you're unhappy with the result, in particular if you realize you don't like the width of the scarf. Think twice, breathe in and out, think thrice. If you're still unhappy, undo what you've done and start again.

I mentioned this before but I must repeat it. Do not waste time working on a project you're not entirely happy with! You may think you've already worked for so long, but you'll regret your mistake every time you look at the end result. So go along and undo your work, the sooner you correct the mistake the better. The good news is that you're a beginner, which means that the second time will be much better and faster. You'll see that in the end you didn't waste any time at all, simply used the first attempt as practice.