The following is a distillation of what I have gleaned from the various quilt books I have purchased and been given since I began learning how to quilt. I hope this proves to be as helpful for you as it has been for me.
Sewing an accurate quarter-inch seam is so important to proper quiltmaking that if you can't manage to do it, you might as well just pack up that sewing machine and take up a more appropriate hobby like, oh, I don't know, making sloppy crap. Because your entire worth as a quilter depends on this skill. No one wants to see a quilt where corners do not meet precisely on point, where seams are not in perfect alignment. Try to give a quilt like that to your mom and she's liable to wad it up, stomp on it, run over it with her car a few times, and deface it with spray-painted obscenities before throwing it back in your face.
So let's get started!
1) Take a look at your sewing machine and note the marks on the needle plate. One of these is marked "1/4". Ignore it. Chances are, you have one of those plastic, made-in-China, bought-on-sale-at-Target models, and everybody knows those are only good for being a doorstop, and they don't even do that well. That 1/4-inch mark was placed there by a godless commie who would like nothing better than to see you fail. Trust us, it ain't accurate. Come back after you've mortgaged your house and bought a real machine, preferably one with an unpronounceable name.
2) Okay, now take a look at the needle plate on your new machine and find the 1/4-inch mark. Ignore that one too. Oh, hush. At least you have a decent machine now.
3) Take a ruler, preferably one you use for cutting fabric and place it on your machine under the needle. Lower the needle carefully and adjust the ruler so that the needle just touches the 1/4-inch mark. Using the edge of the ruler as a guide, lay a piece of masking tape on the bed of the sewing machine, marking a line 1/4-inch distant from your needle. You can now use this line as a guide when you sew.
4) Oops! Forgot about that pesky bobbin thing. If you don't want to re-calibrate every time you change the bobbin (and we can't understand why you wouldn't, but whatever), you'll need to buy a quarter-inch presser foot. We'll wait while you compare the cost difference of replacement feet for your brand new shiny Nordic machine and the one we made you throw out in shame.
5) Once you figure out how to put the new foot on, you'll have to make sure that your machine, if it has multiple stitch settings, is set on the correct stitch for this foot. Otherwise as soon as you start to stitch, the needle will hit the foot and there will be terrible noises and lights flashing and things beeping, and you'll probably ruin your needle, if not the whole machine. We do not speak from experience. We have heard of someone this happened to, a friend of a friend. Loser.
6) If you are certain that you will not bring about the apocalypse when you begin sewing, you will need to test the accuracy of your new foot. Take a 2.5-inch wide strip of fabric and cut it into 2 sections that are 1.5 inches long each and one that is 2.5 inches long. Of course, this depends on you being able to cut accurately. You can do that, can't you?
7) Oh, for fuck's sake.
8) Look. We appreciate the fact that you want to take up this most noble and elegant art. But you're clearly not cut out for it, so to speak. Just hand over that nice, new machine and we'll never let on to anyone how much you suck.
9) Fine. You leave us no choice. We're calling your mom.