The hiding bit is probably the easier side of being a sniper, getting in and being able to wait for the opportunity to act and then get out of the position is the clever bit.
Apparently being a sharp shooter is often seen as being a sniper, but the latter has far more to do than just shoot someone.
Shape, Shine, Shimmer, Silhouette, Shadow were the five basics I was taught as a young Cadet, from that it was easy to "disappear" into the shrubbery, and having managed to "hide" a LWB land rover in a copse so it wasn't visible from 50mtrs was quite an achievement for 6 teenagers.
A thermal imaging scope would probably made these guys easier to find, after all it isn't just about not being seen, it is about being able to see and observe all around.
I'm with Widu on this, easy enough to hide in most rural locations with a bit of sacking and natural material, even kids can do it.