It’s always good and important to sew tzniusly. You will be amazed at how dressing tznius is better. It may seem that some necklines aren’t tnius, but if you make them higher and / or more shallow then you can have any style neckline you like and still keep it tznius. If you want a deeper neckline, you can put a panel in, which I demonstrated on an earlier blog.
A scoop neckline is a circle neckline and is good for school or work.
A boat neck is similar to a scoop neck but is shallower and looks a little like a canoe. It is also good for school or work and it looks nice at shul.
A square neck can be deep or shallow, but has sharp corners like a square or rectangle. It is dressy and better for parties. It takes a little bit more time and planning to make it tznius, but it is really neat when it is done.
A V-neck looks more like a shallow ice cream cone when the shirt is on the hanger. It is good for summer, Bas Mitzvahs or shul.
Turtle neck is higher and is great for winter in shul, at school, in the snow, or anywhere else you want.
It is wonderful that you introduce this topic of necklines.
There are wonderful resources out there based on halacha that clarifies what a kosher neckline is supposed to be.
Here are a few realiable resources:
The Tznius Handbook, http://www.feldheim.com/the-tznius-handbook-educational-diagrams-for-women-and-girls.html
Tznius is a virtue and may Bnos Yisrael merit to keep this mitzvah beautifully.
rochel, try the editor board next year for fashion page you will love it !