I don't pretend to be an expert with leggings but I have found a few ways that I like to wear them and thought I'd share because they really are such a great tool. If you don't own any, I would start with basic black ones. Black goes with everything and will feel more like "pants". Check Maurices, TJ Maxx, Forever 21 or H&M. If you want to spend a little more for higher quality, I hear the Victoria Secret ones are amazing.
Now, on to the outfits. My favorite way to wear leggings is under a basic dress. There are so many cute, little dresses out there that can be super cute with leggings (and it helps to be more modest if the dress is a little short). Over the years, I have found (what I refer to as) Tunic dresses from various stores and those are my go-to for leggings. Sweater dresses are also a big hit and something to pair as well.
One trend that I currently like is the shirts (or sweaters) that are longer in the back than in the front. I love this because I don't like to wear leggings when my lower half isn't covered so this is perfect. These shirts and sweaters also look great paired with skinny jeans, fyi.
You can always wear long tank tops under shirts to add coverage as well so I highly recommend investing in long tank tops (check same stores).
The long, trench-coat look is also in style but in a lighter, sweater-ish way. There are tons of different styles of these - some are more sheer, others are heavier material. These are totally great with leggings because they allow you to wear basically any shirt with leggings as the trench covers the backside.
I got this long trench at Macy's on clearance for $20 but I have seen them everywhere so they are not hard to find if you want one. =)
One look that I didn't do was a skirt with leggings because I'm sure you guys can figure that out on your own.
Keep in mind that leggings are a summer item as well! I just fold mine under a few inches to create the capri look and voila, you still have the cute, modest look in a summer way.
I hope this helps give you ideas for ways to wear leggings. Let me know your favorite way to wear them!