First of all, this is my first guide, i know it's kind of too late because Third jobs are already came out. but for those still looking for sniper guide, you can look and give it some try.
Sniper's is known by one of the faster Dealing damage per second [Double Strafe] but not at all jobs can kill just by DPS or Damage per Second, so thats why here are the other techniques or strategy that i will share to you guys.
SKILL BUILD:
Owl's Eye: 10
Vulture's Eye: 10
Double Strafing: 10
Arrow Shower: 9
Attention Concentrate: 10
Skid Trap: 1
Land Mine: 5
Ankle Snare: 5
Sandman: 5
Flasher: 1
Freezing Trap: 5
Remove Trap: 1
Beast Bane: 1
Falcon Mastery: 1
Steel Crow: 10
Blitz Bit: 5
Detecting: 4
True Sight: 10
Falcon Assault: 5
Wind Walk 10: 10
EQUIPS:
Head Gear: Ulles Cap
Middle: Binoculars
Lower: anything
Garment: Wool/Diablous Mant [Marse/Jakk/Noxius] switching
Armor: Tight/Diablous Robe [Peco Peco/Evil Druid/Marc] switching
Shoes: Tidal/Diabolous Boots [matyr]
Accessories: 2 gloves or Orlean's Glove [Zerom Card]
Weapon: +10 double bloody double boned composite bow [for DAMAGE]
+10 bow[savage babe card/snake card/magnolia card/metaller card.] status bow
+10 bow [2 marina card and 2 plankton card] for immobilizing.
P.S: The reason why the 2 bows that i used is to easily switching. by the way this is the exactly my sniper equips . 
STATS BUILD.
Dex: 84+66= 150 [with bless]
Agi: 90+42= 132 = 183.5 ASPD [with agility buffs and awakening]
Vit: 42+8= 50
Int: 44+20= 64
Str: 11+19= 30
Luk: 1+13= 14
Stats Reasoning:
Dex is need to be 150 because of Damage output, and also for casting and boosting damage of traps.
Agi, actually i am not looking the number of agi but for my ASPD with 183.5 is enough to spam 3 DS per 1 second, and can lay traps at maximum speed.
Vit is for surving, but im not rely on vit because of Acid Demonstration, [its hurt] exact 50 vit is enough to survive SG and Firebolt of mages . and Status Ailments Resist also.
Int is for SP, spamming DS and using True Sight is very SP cost skills, and also boosting the damage of Falcon Assault and Traps . 
Str is for carrying Potions, arrow, Equips etc .
Luk obviously im not Crit type :d
SKILLS THAT YOU NEED TO LEARN:
NOTE this videos are not mine, but it will help you a lot.
Trap Stacking:
Ragnarok sniper fast trapping tip
Trap Stacking 101
Sniper Tactics 2
ARROW SHOWER DANCE
Sorry if I dont have any videos of that skill, but arrow shower is like of occult impact by Champions or Bowling Bash of Knights, it is the animation cancel. Arrow Shower has a Animation after they cast and its prevent spamming of Arrow Shower even though Agi can help a little bit to remove that animation delay, but hell who are stupid to max out agi to reduce that animation?BTW back to topic, after Arrow Shower cast you can walk to cancel it and again to cast another Arrow Shower Immediately, unlike normal spamming of Arrow Shower 2 to 3 Arrow Shower you can cast but after that he delay will trigger, unlike this technique can continue or chaining the Arrow Shower contineously, this is possible if you practice it patiently. Try to watch this video to help you give an idea what i saying.
Ragnarok Occult/investigate dance/cancel
Evil Kanevil's BB dance
STRATEGIES:
For newbies Characters and players, Spamming Double Strafing = Toast. But for Average and Pro players, you must put some new to your Strategies.
White Smiths/Master Smiths:
Just lay Ankle Snare to their path and if they trapped dont ever stand in their front at the range of 4 cell, they can stun you [hammer fall] or if ur in badluck Cart Termination will toast you, some of situation of mine they can reach me at that range. Try to spam DS while he/she trapped by the Ankle snare. But if they dont, try to immobilize her/him [Frost of Freezing trap or Sleep of Sandman] if they inflict, now do the Trap Stacking. At my build 1k each of land mine will inflict them, means 10 Land mines = 10k + my Falcon Assault = Toast . or 10 Land mines +2 DS + Falcon Assault = Toast.
If they Got Immune to Sleep and They cant Frost its either he/she using Evil Druid card [use Silver arrow. /GG] or Marc card [use wind arrow] and use Double Strafing and he/she will Toast . PROMISE ! 
Creator
This is a tough fight, Acid Demonstration will toast us, haha especially at my Build 50 vit is so high for acid demonstration especially sniper cant put shield when attacking, Creator have a high amount of int and vit means resistance of status ailments are good, but we dont have a choice, try to spam DS, and pray they die. haha! if dont, we have a diff, strategies that we may apply.
1st inflict sleep and freeze by immobilizing bow, dont use normal attacks to inflict but try to use Charge Arrow, why? it wll prevent spamming of AD, we can shoot charge arrow at the same time, so the chance to inflict the status is not bad. and again if they get freeze or sleep time to lay traps 10 land mines will damage of 10k but use maybe 4 land mines and at the top of stack traps lay 1 sandman or freeze to remain the target immobilize [dont use FA yet to trigger the freeze or sleep] and repeat it again that set of trap and if you thin you can kill it that set of traps finally follow quickly the FA. if they have a homun and the creator get status kill first the homun.
High Wizards:
At the Right Equips and Build this Character will easily Pawn by Snipers, just Spam DS and it will toast. just careful because sometimes they are using Stone Curse to their armor, in that case use ur Evil Druid armor and muff with marse for SG.
Professors/Scholars:
Men this is tough fight! They can Dispel you, they can provide Wall of Fog or Blinding Mist which is reduce long range attacks about 75 %? im not sure about it free to correct me. I know this character have a high Int and High Vit and it will ruin your status ailments like sleep and frost. Just try to stand at the maximum range and try to inflict them sleep or frost, if he/she inflict sleep or frost now do trap stacking, dont be fool try to kill the target by using DS, try to stack about 4 land mines and at the last stack of trap is put sandman or freezing trap for after the land mine will blast the target can be remain at sleep or frozen status then repeat that method and if you think she/he can kill last set of traps try to follow an FA to make sure she/he will toast.
High Priest
Men Dont be full try to kill this, what ever methods we do we cant kill this. haha!
Champion:
My one of favorite opponent , dont chase them. let them chase you. try to spam DS and if they kill maybe he or she is noob but if they Pro Dont waste your SP for DS, try to inflict them immobilize status,if they use pneuma at that time use +10 bow [2 marina and 2 plankton]. and if they inflict just lay 10 land mines and sure after you complete 10 land mines the pneuma is gone then trigger the mines and quickly follow FA and they toast . if he/she cant sleep or frost, again maybe he/she using undead or unfrozen and it is more easily to kill with our elemental arrows, if the use their pneumas use tour +10 bow [snake/magnolia/metaller/savage babe] and wait and wait and wait to inflict any status and and hope at that time the pneuma is gone and spam DS . especially when the target is stun or silence.
P.S dont lay Ankle snare because of Snap the cant walk but they can still sue snap, use Skid trap at your near and step it as escape mechanism if the champion get near you by snap. hihi. or Charge Arrow .
Stalker
This section will be a battle of the brain, because a lot of build that stalker can be possible, but dont be too much scared of Full Strip, because we are sniper are dominant when we speak Dex, and we cant easily stip, but if stalker get Link naaaah that is danger . but if we have a FCP dont be afraid .
Again try o kill them with our Spamming DS. 3 DS/sec and if they cant kill,again immobilize them and lay traps, if they using Chase walk use Arrow Shower Dance for fast Detecting, and font forget use Status bow or Much Better Immobilizing bow, and when they use hide ofcourse we have a Falcon to detect them:)
Assassin Cross
The most my favorite opponent . if the cloack use Arrow Shower Dance, with status or immobilizing bow, dont waste your SP for Detect. tsk! use it if they try to hide especialy when they try to Grim tooth. They toast if they try to use undead or unfrozen armor, haha ! just to spam DS or even they use shield and at the same time they use that armors, still = toast if they dont get that aromors inflict them sleep or frozen and lay traps + FA and toast . of course we need to put undead armor remember, we are not alone can use status weapons, with throw venom knife, sinx can inflict status also.
Paladin
Dont try to kill this with your DS haha ! chaining trap stacking can be possible to kill this, but it will possible if he/she has no immunity for sleep or freeze, but we need to accept that being snipers we cannot kill all RO Characters. agree?
Lordknight
Also this but the chance to kill this against paladins are more possible, it is because if they are using 2 handed sword,means they dont have shields unlike paladins, try to use chaining trap stacking until they die, but again it will possible if they dont have immunity for sleep and freeze. And one more if someone try to kill you at Berserk mode, he /she is FOOL! lay ankle snare at his/her path and if they got Spam DS untill they Toast. hahah !
Sniper
An endless Battle. Just because the strategies of one of them can copy by his opponent which sniper also. hahaha ! GoodLuck !
Feel to put your comments, suggestions or even criticism. :p but the main reason why i wrote this guide is for those trying to look the full potential of being SNIPER. and not just rely ONLY to Double Strafing. That's all and Thank You
SHOOT WELL.
