This is an older post that has some great tips on how to alter tulle or netting on your dress.
After reading this post, click on How To Hem a Dress with Tulle or Netting for an updated version.
This particular dress, below, had two layers of satin and two outer layers of netting on the skirt part of the dress:

so I folded up the amount needed and pinned it in place:

as you can see, the amount that needs to be taken up is not even all the way around:

So, I couldn’t just cut off 2 inches.
I had to find a way to mark the new line.
If your netting (or tulle) is made of polyester, you can just use the iron and press the folded edge like this:

However, if the content is acrylic or acetate or some other heat sensitive fiber, I wouldn’t iron on it.
In fact, always test the iron on a section of the netting that you’ll cut off anyway to make sure your iron is set at the right temp before going on.
If you have a heat sensitive netting, I would hand baste a long running stitch to mark the line. Use a dark color of thread so it will stand out for you.
Once you have marked the line, slowly and carefully, cut the edge with a sharp pair of scissors:

On this hem, I decided to keep the hem folded because I was concerned that if I opened it up, the two pieces might move apart and then it would have been difficult to get it lined up again exactly where I had it.
If you are a little uneasy about this, just practice on a scrap piece of netting first.
Just as I was getting ready to cut the netting, I got an e-mail from Christy.
You remember Christy. She owns an alteration shop in North Carolina.
She gave us the great tip on using rings when making a French Bustle.
Well, she told me that she now cuts her netting with her serger!
Wow, I am not that brave yet, but I think it’s a good tip, especially if you are taking the exact same amount off all the way around your dress or veil.
Just take all the thread out of your serger and use only the blade to cut the tulle:

She said it may dull the blade a little, but a new blade is worth the time it saves her from having to use scissors.
Give it a try.
(Of course, you’ll want to test it on a scrap first.)
Whether you use the serger or scissors, your hem will be just as straight as the satin hem below it:

If you are creating a gown from scratch, you can always use the rolled hem foot on your serger to stitch a decorative edge on the netting, if you wish.
I have done that when making bridal veils and it is very pretty.
You can experiment with the tension, stitch width, and stitch length to get just the right look.
Have fun with it.
Thanks Christy!
And don’t forget to jump over to the post on How To Hem a Dress With Tulle or Netting!
Could you be more specific on how you use a rolled hem foot on your serger to trim a veil?
thanks so much