First off sog depends purely on timing if you have NO timing what so ever, forget about this technique. Keep in mind that elves range takes about .5 seconds after you click, so elf sog is known harder. But as soon as you master elf sog... You will become invinsible i guess, Rank 1 range+Rank 1 Magnum+A bunch of dex+Sog=Awesomeness. Now how to do sog. It is very simple and over thought, although i cant do out of range sog... i can do in range. There are two kinds of sog, The counter sog and then timing sog. The counter is when you use the percentage shown at the top of the skill and fire at say 26%, and you never miss there(everyone has their one counter percentage, mine happens to be 30%~32%). Then the timing sog is when you use say... Magnum, as soon as you bounce up from holding magnum you shoot. Right in the middle of the bounce is a perfect sog. There is also the very hard (i think) Fast sog. You fire the arrow immediately, as soon as you load it. This requires no lag and is very tricky, sometimes you have to fire it later and other times you have to fire it asap. Well good luck and also try this video it helps explain sog a little better than me.
Thank me if i helped :D