This is a very simple way of creating fullness in the neckline of a dress or t-shirt without having making the item baggy and ill-fitting lower down.
There are two ways of doing this, but it's probably easiest to cut the front pattern piece on the folded edge of the fabric, so if it is a full piece, just fold it in half from top to bottom (vertically through neckline).
Fold your fabric (right sides together) ready for placing the front pattern piece. Then, instead of placing the middle front along the fold in the fabric, just move the neckline away from the fold as shown below. Keep the lower edge of the t-shirt or dress against the fold (unless you want to alter that as well) to create an elongated 'V' shape between the pattern piece and the fabric fold.
Move the pattern piece further from the fold to create fuller gathers (remember it is folded so fullness will be multiplied by 2 when opened flat).
Keep a note of the distance from the folded edge to the pattern piece at the neckline. This dress was 6cm to the fold making a total of 12cm extra fabric to be gathered.
You could pleat the neckline if you prefer...
Mark with pins where you want the gathers to begin and end (equal distance from each shoulder seam). I had already sewn the dress together at this point so I could try it on, but this step can be done before assembling the garment. The two middle pins are not necessary in this picture.
Gather with a long machine stitch between the pins.
And finish the neckline as you like. I used fold-over elastic (FOE) for this stretch-knit dress.
Here is the finished neckline. Remember I moved the pattern out 6cm from the fabric fold. Use this measurement as a guide to work out the fullness of the gathers you would like in your garment.
I will show you more of this dress soon. I am very happy with how it turned out!