V-neck Tutorial

This tutorial is geared to assist in the construction of the Primrose Pullover by Cali Faye Collection.  If you are using this tutorial for a design other than the Primrose Pullover, please keep in mind that the V is on the BACK BODICE of the Primrose Pullover.  If you are constructing a design with a V on the front bodice you will need to take care not to confuse the front and back bodice terminology of this tutorial.  
The fabric I am using for this tutorial is a french terry knit, with 50% stretch from Knitpop.com.
The Primrose Pullover is best paired with durable knits or textured knits of light to medium weight with at least 50% stretch and 100% recovery.  Some fabric choices to keep in mind are ponte, tricot, sweater, hacci, pique, stretch velvet and double brushed knit.
We will begin this tutorial with the assumption that you have cut all pattern pieces and the front and back bodice pieces have been joined at the shoulder and side seams.  
Bring the ends of the V-NECK COLLAR piece together, RSF.
Fold the end lengthwise to match all the raw edges along the slant.  

Join the slanted edge together with a 1 cm (3/8") seam allowance.  

Neaten the seam to reduce bulk.

Open the V of the collar and maintain the natural fold it created around the collar piece. Press the seam flat.

Make an indication 1 cm (3/8") above the base of the V on the COLLAR piece.
Make an indication 1 cm (3/8") below the depth of the V on the BACK BODICE.

Apply a stay stitch 1/2 cm (1/4") from the raw edge on the BODICE around the collar line. Do not backstitch.
Apply a stay stitch at the base of the V on the V-NECK COLLAR piece. You will need to ensure that this stay stitch does not exceed 5 cm (2") from the depth of the V. Do not backstitch.
Make an indication at the position directly opposite the V on the V-NECK COLLAR piece and at the center position on the FRONT BODICE.  Use these two points as matching references later.

Align one edge from the V of the collar piece to the V of the bodice collar. Use the previously indicated 1 cm (3/8") distance indication markings as matching reference points.  

From the 1 cm (3/8") marking apply a basting stitch a few inches into the neckline.

Manipulate the V-NECK COLLAR piece to the align the opposite edge of the V to the collar line.  You might have the urge to clip the fabric at the V of the collar line to allow the fabric layers to ease into shape but I want to insist that you DO NOT clip any portion of the collar line at this point!

Apply another basting stitch along the collar line to temporarily join the pieces.  

Turn the collar right side out to get a preview of the V of the collar.  Is the V centered?  Does the fabric buckle?  If so, pluck your basting stitches out and redo the process until you've got it right.

Now, match the center of the FRONT BODICE collar line to the indication directly opposite of the V on the collar piece. With the front and back bodice collar line matching up to the two positions on the collar piece you can evenly distribute the length of the collar piece to the collar line.  

Evenly distribute the collar length.  Use several pins to keep distributed lengths even and in place.  
I've used a fairly stretchy fabric which has made this process super easy. If your fabric has less than the 50% recommended stretch then this process may be more difficult than intended. If you find that the V-NECK COLLAR piece is exceedingly difficult to manage you may need to recut another V-NECK COLLAR piece with added length to compensate for the lack of stretch. 

Apply a basting stitch around the collar line to temporarily join the pieces.  Leave at least 15 cm (6") of thread at the beginning and end of the stitch to allow you to distribute any kind of bunching around the stitch.

Turn the collar right side out to ensure there isn't any puckering in the collar line.  
Puckering happens when your fabric was overstretched in one position and not stretched enough in another, or when a layer of fabric folds over itself while joining pieces. In the picture below a piece of the bodice collar line folded over itself and caused a slight pucker.  
To remedy this, remove just enough basting stitches to evenly stretch the collar line flat again.  There is no need to apply an additional basting stitch unless the length is excessive. In this case I was able to remove 6 stitches to evenly spread the fold.  This happened four times during my basting stitch and was easily remedied with minimal effort.  

When you are certain the collar line will finish smoothly, permanently join the collar to the bodice with an overlocker, serger, or the overlock stitch or tight zigzag stitch of a standard sewing machine.  Remove all basting stitches.
Give the collar line a nice press and you're done!

I let V-Neck collared designs keep me away from making specific outfits for years! This is not an easy process and it may take you many attempts at a V-neck before it looks perfect. Don't let that keep you away from giving it a try though! It's just another skill to add to your sewing skill set.  
Good luck!