This is the type of stone I used, they are available in many different shapes, sizes and colours. These ones are sew on - you can see in this size there are 4 small holes on the underside of the metal casing which are invisible when you look at the stone straight on so are great for decorating garments. I've threaded a needle through the top set of holes in case you can't see them.
My dress was made of wool which was sturdy enough not to need additional interfacing, although a lot of the stones were on part of the neckline that was faced anyway. With lighter weight fabrics or a lot of stones you may want to make sure that the area to be embellished is strengthened either separately or as part of the design - e.g. a neckline band, waistband, yoke.
Here are a couple of RTW examples I found on my internet travels.
I also found a great site for inspiration shopping - Shopstyle, you can look in specific categories or search on key words - lots of good stuff here!