Stripes are a perfect basic print but sewing with them can be a challenge. You almost need to make your own clothing nowadays, when it comes to stripes, to ensure that they match up. Here is how I make sure the stripes on my clothing match up. I'll use leggings as an example
Generally you cut leggings with a double thickness of fabric. When I'm working with stripes, I open the fabric and cut each piece one at a time.
Once the first piece is cut, I unpin the fabric. Then I place it on top of the opened fabric, just a little way from the cut-out. I match each stripe on the cut piece to the stripes on the uncut fabric. The cut piece serves as a template. Pinning it down ensures that the fabric will not shift while carefully cutting around the edges. I outlined the previously cut piece so you can see it.
When sewing, go slow and ensure that your stripes stay matched up. Pins can help. I like to not use them, when serging, so that I can better see what the stripes are doing. Knits do tend to stick together nicely.
Here's a close-up look at the back of the finished Navy Sailor Stripe Organic Leggings (which will be available Monday evening):
NOTE: Sometimes it is possible to fold fabric so that the stripes match up, especially with wovens. I've found that the stretch in knits makes doing so difficult, which is why I use this method. It also allows me to check the stripes on either side of the pant more easily.