These instructions are for intermediate skill, involving some pattern manipulation and the knowledge of how to piece together shirts, specifically collar and sleeves.
Leia's shirt is made out of a beige/khaki fabric, probably a cotton twill or bottomweight. It is fitted, has a lapel collar, and the sleeves are elbow-length, are folded up, and have a pocket on each sleeve. It closes with snaps, and there is no evidence of top-stitching. My pattern I draped and drafted myself, and I think it is fairly close to the original, even in proportion since I am the same size Carrie Fisher was. You would, of course, pattern to fit your own shape.
You will have the following pieces:
These are the flats I drew of what the pattern pieces are shaped like... this is not a to-scale sketch, just a guide. There aren't seam allowances drawn on here, so don't forget to keep seam allowance into account when patterning. Technically, all seam allowances should be 1/2" (unless you are using a commercial pattern, those are usually 5/8"), except the neckline and pocket parts, which would be 1/4". Click for full view.
I highly recommend always making at least one mock-up of the shirt for fitting purposes first. If you don't know how to draft or drape, you should study Leia's shirt and the pattern flats I have provided and find a similar commercial pattern to alter. I recommend trying to find a pattern that mostly matches the collar shape as the other elements can most easily be altered.
The shirt should be fitted (not skin tight, but slim to body) because it tucks into the pants and you want as little bulk at the waistband as possible. You can draft your own or use a commercial pattern and alter it, and what body darts you use doesn't matter; it won't be seen. I used simple front darts, larger busted gals might want a side bust dart as well. Back darts can be added if needed as well. I found one pattern that would work for the shirt, with collar and sleeve modifications. McCall Pattern 5138.
Your shirt front will need to extend 1/2" from center front for an overlap. For the collar to be shapped correctly, the center front at the top will need to be a square 90 degree angle. Most patterns look to have a bit of a slope here, but this will need to be completely straight for the first inch at least. You will also need a facing because the collar will fall open. If your pattern doesn't include one, they are simple to make. On some scrap patterning paper, lay down your shirt front pattern and trace the shoulder, neck, front and the first 3" of the hemline. Now, along the neck and shoulder, draw in 2.5" until you get the facing pattern I have shown. If you closely observe the pictures of Leia's lapel, you will see no seam where the shirt front attaches to the facing. Usually shirts have them separate and sewn on, but to be accurate for this one, take your facing pattern (be sure there is no seam allowance on either the front or the facing), flip it, and tape it to your front, as you can see in the sketch under the colored shirt. I showed both ways in the pattern so you know how to pattern it, though you should have the separate facing pattern to cut out your interfacing. The shirt should probably extend to about the hips so when your arms are lifted if, say, you place your hands on your head because you've been captured by Imperials, your shirt won't become untucked. A 3/4" - 1" seam allowance should be added for the hem.
Next is the collar. This collar is a pretty simple shape. The front of the shirt extends 1/2 inch from center front, your collar will end 1/8th inch short of center front (basically, measure 5/8" from the front of your shirt.) The top and sides of the collar are completly straight. There is a slight curve on the bottom sides. You will probably only need to straighten the lines indicated on the pattern.
For your sleeves, you will want something with no extra gathers into the cap. For a clean ease, the sleeve cap should measure between 1/2" and 1" longer than the combined measurement of the armholes on your front and back (minus seam allowance). If your pattern includes no gathers (aside from easing), don't worry about it. You will want to straighten the sleeve if it tapers in at all; her sleeves are comfortably loose. Measure from the top edge of your shoulder and measure down to the top of your elbow. This will be your sleeve length (the first line on the sleeve pattern provided). Her sleeve will fold up. Since there aren't many pictures where you can see the fold clearly, guesstimate how much it needs to be folded up. I think between 2.5" and 3" is your best bet. You will extend your sleeve by that measurement, and then extend it again since it will be double folded.
For the pockets, I have taken the liberty of making a printable pattern. The pattern should work for everybody, but is easily adjustable if you need a different proportion. The pattern and instructions will be available shortly.
First, cut out your pattern and your interfacing. On the back side of your front shirt pattern, iron on your fusible interfacing. Featherweight to medium weight is what should be used. If you have a serger, serge the edge along the facing. If not, finish the edge in the method of your choice. Fold back your facing and press. Sew in your darts as well. Sew together your front pieces to your back piece.
Next is your collar. Iron on your interfacing to the back side of one collar piece, and make a mark at the center bottom of your collar to note which side to leave open. I'm an experienced seamstress, and I still sewed it on the wrong side the first time! Leave at least 1/4 inch from the bottom open when stitching. Clip the corners, turn and press. Attach the bottom of the collar (the non-interfaced side) to the neckline, matching center collar and center back of the neck. The collar should end 5/8" from the end of the front neckline. You will clip your front neckline on the shirt a bit where your collar ends, and you will tuck the excess into the front of the point and press. The rest of the seam will be pressed up, the inside of the collar turned in 1/4" and hand sewed to the shirt to finish it.
You will want to assemble your pockets before you assemble your sleeve. It is much easier to attach your pockets to the sleeve while it is still flat. The pocket pattern is a bit involved, so I'm putting it on it's own, picture-intensive page.
>>Click Here for Printable Pocket Pattern
Take your sleeve pattern, front of fabric facing up, and fold up on the first fold line. Fold up again on the next fold line and press good. Fold your sleeve in half and crease or mark where the center of the sleeve is. Do the same with the pocket to find the center. When placing your pocket, note the reference pictures. There needs to be enough room for the sleeve cap on the vest, and the bottom of the pocket doesn't reach the bottom of the sleeve, rather about half-way down the cuff that was folded. When the placement is correct, in the center of the sleeve, pin the pocket to the sleeve. With the flap up (open), stitch the pocket to the sleeve along the stitch line you already put in the inside of the flap as indicated in the pocket instructions page. Next, by hand, stitch your pocket sides to your sleeve, but only to about 1/2" above the top of the cuff. The pocket is not attached all the way down. In some shots, the cuff is under the pocket, and sometimes the pocket is under the cuff. To keep the flap down, I added a couple tacking stitches at the top of the flap in the down position.
Once your pocket is on, you finish the sleeve like normal. Match side seams and sew. On mine, I turned the seams in towards each other and sewed, making what's called a False French Seam, and finishing the raw edges.
If you aren't very familiar with easing in a sleeve, here's basic instructions. You will sew a basting stitch at about 1/2" along the sleeve top. Do not backstitch or knot thread, and leave the ends long. Turn the sleeve right side out and the shirt wrong side out. Match your shirt side seam to your sleeve side seam and pin, and pin the center of the top of the sleeve to the shoulder seam. Pull your gathering stitch and gather up the fabric so the sleeve is smaller than the armhole. You will then start moving the gathers out and smoothing them. You don't want puckers on the stitching line, but you should notice the outside of the seam seems to ruffle a bit. Most of the gathering should be confined to the cap of the sleeve, and it should be smooth near the armpits. Start pinning from the bottom up, smoothing your gathers out until the sleeve and armhole match up. Once everything is pinned, sew (being careful of creating puckers). If you can, serge the edge. If you have no serger, you can stitch another line a tiny bit further out from your seam and trim your seam allowance.
Now your shirt should start looking like something wearable! You will want to match up the front of each side of the shirt to make sure they are the same length, and hem up your shirt. Put on your shirt. The closure for this shirt should be snaps, as there are no buttons visible on Leia's shirt. It closes right over left. You will need to start by finding where the center of your bust is on the front; this is where the most straight would be on the closure. When buttons or snaps are placed not at center bust, gapping can occur. Next, study Leia's shirt to see where the lapel starts to fall open. No cleavage is showing, so there should be a snape placed a but above the topmost point of the bust. Your proportion is what determines how many snaps you need to place. I didn't need to place another snap between center bust and the top snap, but larger busted gals might need to. I used the distance between those two snaps as the increment measurement between snaps, and I used 5 snaps. This is the last step to finishing your shirt :)