I'm still a newbie, but where I play is an 80 acre parcel of land that is mostly man planted (in rows) pine forest that is very mature. Because of this it is all shaded and there isnt much large brush (4-7 feet tall) but there is plenty of ferns. Due to this fact Gillie suits wouldn't help much. So my tactic is to use the lines of trees as cover and stalk up on my target. What has seemed to work best for me is to stay low and use a 'move 5-10 steps, then take a knee and look/listen'
I also like to use the high ground as an advantage. just take a knee or go prone and fire on someone, when they figure it out retreat to the other side of the hill and take cover. watch for them to come over the hill (their silhouette will give them away) and place a shot in their chest.
-Another tactic if you dont mind taking the time to set it up is to make a pile of pine needles/leaves and then put yourself in it. works great for a one time sniper shot but once you are found out you better get your arse outa there fast.