I know people have different understandings and may not agree with my convictions or understanding of Scripture. But I'll share them anyway for anyone who wants to listen.
My guideline verses:
1 Timothy 2:9 & 1 Peter 3:3&4 about modesty and not wearing costly or extravagant clothes/decorations
Deuteronomy 22:5 The woman shall not wear that which pertains to a man. This is where many don't agree, and they will bring up culture and what men and women wore at the time it was written, etc. How I see it is there was always a distinction. And I look into history and where pants-wearing began for women. It began as practicality because the women were trying to compensate for the men being at war and they were doing their factory jobs and such. Then there was women's suffrage where they wanted equal rights, and pants-wearing for many was a sign of (I'm gonna step on some toes here) rebellion.
(Of course, I'm not judging anyone's heart here because of what you may or may not wear, so there's no reason to be offended.)
Here's another scripture that gives us a glimpse into God's view of modesty: "Come down, and sit in the dust, O virgin daughter of Babylon. . .uncover thy locks, make bare the leg, uncover the thigh, pass over the rivers. Thy nakedness shall be uncovered, yea, thy shame shall be seen. . ."
My family used to dress VERY conservatively, similar to the Amish. but in the last few years things have changed and we've realized it's not necessary to dress quite like that to please God and not cause anyone to stumble.
I truly believe if each of us really seek God with an open heart, He will show us how He wants us to dress. And another thing I wanna say, you can "look the part" and be completely "modest" the outside, but your heart be far from modest.