I dont have deep knowledge from Sniping as the one that made that guide on the link, but there are some few things that could make a direct impact on your gameplay, with any gun you use, but for a Sniper Rifle I guess it could help some more.
First make sure to know the map you are playing, entrances, hallways, corners, common choke points, this becomes useful when you are trying to lead what the opposing team is trying to do or going to. Using this along with checking your minimap as much as you need, knowing what places is safe to go or not (if there's no teammates around that zone, assume it may be used by the opponent), for both T/OSOK and CTF its about map awareness, for public games it may be more intuitive, as for clan matches its more about using strenght on numbers (teammates) so it wouldn't be so hard to spot enemies (TS) neither cover good portions of map having a good sense of where to push or where to put your focus into.
About aiming, this just doesn't come by doing something specific, if you feel awkward when moving your mouse or have issues, no matter what somebody tells you, is not going to work, get used to whatever number you have and see what lacks on your game when approaching to opponents under different circumstances then decide whether increasing or reducing your sensitivity value is a good idea and suits your play style. As for head shots, something that does work for some people is to have a specific height above the ground level to have a reference on the player's head, if you can implement that on your game and feel comfortable with it is no harm really.
Reflexes, quick movements and the like come through experience, so it sums down to that and eventually will give you an extra plus when both you and the opponent are about the same level.
last but not least, know your role, sometimes people tends to despise defensive players because they focus on the fragging part of the game, if you feel comfortable by doing so don't worry about it, both ends attacking and defending are equally useful depending on the moment of the game, this means at some point you may play this role by holding an area of a map (for example ac_depot middle point) allowing your teammates to push inside the enemy base while you provide cover, its never a bad idea to switch spots so you don't grab too much attention and keep them disoriented.
I can't think on anything else for now, i guess there may be more into it but for new players it may be a good starting point.
First make sure to know the map you are playing, entrances, hallways, corners, common choke points, this becomes useful when you are trying to lead what the opposing team is trying to do or going to. Using this along with checking your minimap as much as you need, knowing what places is safe to go or not (if there's no teammates around that zone, assume it may be used by the opponent), for both T/OSOK and CTF its about map awareness, for public games it may be more intuitive, as for clan matches its more about using strenght on numbers (teammates) so it wouldn't be so hard to spot enemies (TS) neither cover good portions of map having a good sense of where to push or where to put your focus into.
About aiming, this just doesn't come by doing something specific, if you feel awkward when moving your mouse or have issues, no matter what somebody tells you, is not going to work, get used to whatever number you have and see what lacks on your game when approaching to opponents under different circumstances then decide whether increasing or reducing your sensitivity value is a good idea and suits your play style. As for head shots, something that does work for some people is to have a specific height above the ground level to have a reference on the player's head, if you can implement that on your game and feel comfortable with it is no harm really.
Reflexes, quick movements and the like come through experience, so it sums down to that and eventually will give you an extra plus when both you and the opponent are about the same level.
last but not least, know your role, sometimes people tends to despise defensive players because they focus on the fragging part of the game, if you feel comfortable by doing so don't worry about it, both ends attacking and defending are equally useful depending on the moment of the game, this means at some point you may play this role by holding an area of a map (for example ac_depot middle point) allowing your teammates to push inside the enemy base while you provide cover, its never a bad idea to switch spots so you don't grab too much attention and keep them disoriented.
I can't think on anything else for now, i guess there may be more into it but for new players it may be a good starting point.