i find gathering around the whole of a top like this just feels like a lot to do in one go and get it well distributed around the whole seam. If you don't get on with Jessie's method and assuming you've already joined all the sleeve seams etc., this is the method I would use:
1. Mark the centres of the yoke front and back, put them together so you can then mark the quarter positions on the yoke (centre of the section that is sewn to the sleeve).
2. Now match each pair of marks to make another set of marks between them so you end up with 8 little marks all equally spread around the seam line of your yoke.
3. Do the same on the body of the dress.
4. Sew your gathering threads between the marks in short sections rather than one or two long lengths around the whole body of fabric.
5. Match the marks on the yoke and body and pin them together (at right angles to the seam).
6. Gather up the fabric between the pins, spread the gathers evenly and pin (at right angles to the seam so you can adjust gathers evenly). You can use lots of pins to keep tiny gathers in place and avoid lumps if needed.
7. Machine. You can pull out the pins as they get right up to the foot and, while lots of people don't worry about sewing over pins like this you can easily break a needle so I prefer to hand turn the machine over a pin if I really don't want to remove it before it's sewn down.
It's not as long-winded as the numbered steps appear and has several advantages. It gives you more control more quickly because it gets the long ungathered fabric attached evenly around the seam right from the start so, being fixed in so many places, it won't hang down with the weight of the full body. It's also much easier to gather short sections at a time rather than pulling long pieces of gathering thread and is much more likely to produce evenly gathered fabric around the entire yoke because you're only pulling through one small section at a time - if you pull hard it won't start pulling it through from the next section.