How Do I Make Realistic Jeans???!!

I see several designers have made their jeans look so real.I am a designer myself and I am very good with photoshop but I just cant seem to get that realistic effect.Do I photosource or what????

Yes, I suspect that most good jeans in SL use at least some photosource data. Denim is a difficult texture to get right by entirely synthetic means; doubly so when you want details like fading at the right body parts. You will need to warp the photosourced image to fit the curves of an avatar properly; I don't know of any shortcut for that, but I'm sure that the real clothing experts do The very best ones will also be enhanced with hand drawing.

Watch the seam matching at the sides of the avatar. Many jeans in SL are very bad that way. The trick is to adjust the position of the back and front images to get it right, and you may also have to stretch one of them a bit more than the other. (And even when you get it perfect on your avatar, it might not be on a different shape. So it goes.)