Pencil skirts seam to always be in style, but seem to be coming back with a vengeance right now. I have never been able to buy pencil skirts because of my "curvy" figure. Thank goodness I can sew!!
A pencil skirt should be fitted in the waist, but also in the hips, with enough room that you can still walk, sit, and move! This can be a challenge, so a little fitting work should be done ahead of time. You may or may not want to make a muslin, but lately I've been finding much success with tissue fitting.
In any matter, the most important thing is to start with the right size pattern. I use my actual hip measurement (measurement with the tape measure fitted snugly, but not cinched in.) For me this is a size 16. It seems ridiculous for me to make a size 16 pattern when I wear an 8-10 in RTW, but the tape measure does not lie! If you are between sizes, go up a size.
THen, when I make the muslin, or the skirt the first time (I didn't really need a muslin with the linked skirt since there are no design features such as yokes, pleats, pockets, etc), I cut 1" side seams and BASTE them together and try on the skirt. At this point, you can make any adjutments you need to. On my first version of this skirt I had to really take in the waist and adjust the curve from hip to thigh. Baste it again after you think you have the changes right and try it on again. If it looks good stitch it.
Now, make those exact changes on your pattern pieces. You will only have to do this ONCE. This is the fourth time I have made this skirt, and now it is a breeze to whip up. If I make it out of a different fabric with more/less give, a different drape or thickness, I make it with the wide seam allowances and baste first. My machine makes a long basting stitch that is quick and easy to rip out. It only takes a few seconds to baste it and try it on compared the the many minutes it takes to rip out a perfectly sewn seam!
Another tip, if you are hippy (as I am) it is usually more flattering to slightly peg (taper in to the bottom) your skirts. Straight skirts tend to make you just look hippy all the way down. A tapered line draws the eye inward.