I don't know about you, but gathering is not my favourite sewing technique in the world. As I started writing this, I came across this tutorial on gathering with an overlocker, something I've never tried myself, so if you want to try that method, head on over and check it out. I'm planning on giving it a go in the not too distant future myself.
Here's how I did the gathers on all of my bridesmaid dresses. It's just your traditional sew two parallel lines and pull them up, but I thought I'd try something a little different when pinning the gathers down, and found that not only does I produce more even gathers, but it doesn't take as long.
Before you start, make sure you have a good quality thread that won't break, and have enough thread in your bobbin to go the distance. If you run out of thread, you'll have to pull out your stitching and start again, and you don't want that to happen. I sometimes use a different colour thread in my bobbin and needle thread (I'll explain why further on). I use Gutermann thread for my sewing.
Using a long stitch, run 2 parallel lines of stitching about 1cm apart. I use a 1cm seam allowance for most of my seams, so I run the first line the width of my presser foot from the edge of the fabric (just over 6mm), and the second line at around 1.5cm. If you were using a 1.5cm seam allowance, you would run the gathering stitches at 1cm and 2cm from the edge. For this light weight satin I set my stitch length at 5. For a thicker fabric you might set it at your longest stitch, which on my machine is 6.
Mark out regular intervals to match up on the bodice and skirt, starting from the seam allowance. For these dresses, the skirt gathers were approximately twice the length of the bodice, so I divided both pieces into 16 sections. I start with quarters (ie from centre back to side seam on left and right, and from each side seam to centre front on left and right), and mark each of these four sections into quarters. On the bodice I tend to measure my markings out with a a tape measure or ruler, but on the skirt, or larger piece to be gathered, I simply match up my markings and fold in half, mark with a pin, fold in half again, mark with a pin, until all my sections are pinned.
Here's another dress that I've been working on, where the gather is more like 1.5. Rather than 16 sections, I divided everything into 8 sections.
Match pin markings on bodice and skirt pieces. With right sides together, pin the marked sections together, being sure to align side seams.
Pull up one set of the gathering threads from each end, until the area to be gathered is smaller than the area to be gathered to. Here's where the different colours in your bobbin and needle thread come in handy.You won't accidentally pull up the wrong threads at the other end when you check the colour first!
Don't worry about making the gathers even just yet. I used to use a stack of pins at this stage trying to get my gathers even, and then found that they moved around when I went to sew them down. You'll end up adjusting the gathers as you sew anyway, so why bother trying to get them perfect now?
Sew your seam! Stitch up to your first pin, then remove it so it doesn't get stuck under the presser foot on the way past. All subsequent pins you will also remove as you go.
Pull out the gathering stitches, and press the seam. If you clip the threads in the middle, it will be easier to pull the threads out from both ends.
If sewing a skirt to a bodice, I generally press the gathers towards the bodice, so there is less bulk on the seam. Here I have a bodice and a skirt both being gathered to a waistband, so I have pressed both sets of gathers towards the waist.
Hey presto, perfect gathers without the headache!