Pretty much this, except never invest in earth armor. Waste of money. Now, for a sniper there's a few things you'll want to realize:
You're most likely going to be o/w. You'll want at least 2 different kinds of arrows, for example stone arrows and holy arrows. And you'll want a lot of them. I'd say hotkeying 3 or 4 different arrows is best, though. You're also going to be needing a LOT of traps. I waste hundreds of traps in no time with my Sniper. I think it's ridiculous how there's snipers out there who don't trap, it only takes seconds to learn (lay down trap, arrow shower the cell behind it to drive it forward. If you want to move it up, arrow shower a cell underneath, etc). You'll also want to carry a lot of bgems for safety wall.. Missy ears are definitely not worth it.
For matchups, here's how it goes:
Sniper vs LK - This is a tough matchup. First spiral pierce, you probably won't even know which element it is, so wear angeling. If they switch elements switch to the corrosponding armor. Anyways, as a Sniper, you do not want to get hit an LK, so the most simple thing to do is get them in an ankle snare and go out of their range for things like spear boomerang, charge attack, etc, and shoot them. LKs almost always carry GJ, so there's no point in trying to use shockwave traps. Just DPS them from far, and replinish your ankle snares every once in a while. When they go in frenzy, use the same tactic. If they manage to break out of ankle snare and you missed ankle snaring them again, use a hide clip. When an LK is frenzied, they lose 5% of their HP every 15 seconds and they can't do anything to uncover your hide. So you basically win.
Sniper vs High Wizard - Storm gust has some mean range, and that's what a HW will use. Simply wear wind marc and even if they do hit you a few times, you should easily be able to win (They have lowwww HP). But feel free to use things like bris/rosaries, kapha wool/ragamuffin, and kahos as well as sleips for the mdef.
Sniper vs Sniper - I'm not too sure about this one, but wearing an angeling armor might be your best bet, as well as a noxius garment. This is a kind of weird matchup, I think that you might have to use status arrows to win, and that you'll have to correctly guess the enemy's element (water, wind, etc).
Sniper vs Whitesmith - ankle snare. That's all you really need, I mean, when fighting a whitesmith you're going to scared of them getting close. So push them back and shoot them, or ankle snare them. Safety wall is not a good idea due to meltdown and the fact that Mjolnir has that thunder strike ninja skill. Regardless, wear your wind marc and kick their ass with DPS. Crit/falconlock with anklesnare is very awesome. Beware shield boomerang though, so once you do have them ankle snared, get out of their range or your bow will most likely break. Assuming you're on your last straw, switch to water OL and pop up a safety wall. Maybe the reflect will kill them. This is another tough match simply because of meltdown.
Sniper vs Assassin Cross - First of all, you'll want to switch regularly between poison and ghostring armors. If the SinX is a TF user, you're in luck. Keep safety wall up, and toss on water OL.. Put on poison/GR (corrosponding to their element) if they start grimtoothing you or something. If it's a dagger SinX, you might have some trouble. Especially if they use swordbreaker. If they run a soulbreaker build and SB > Hide > SB > Hide, use a noxius garment. If they're poking at your safety wall with occasional soul breaker, just try your best to outdamage them via DPS / Sharpshooting, and wear the correct armor. You could also get a poison garment, but usually raydric works just fine. Remember that if you charge arrow them, you can always place traps around you. I'd place freezing traps.
Sniper vs High Priest - If you fight a HP who knows what they're doing, you won't win. But generally, this is what you want to do. Ankle snare them, safety wall them (before they can pneuma themselves), toss two shockwave traps to get rid of their SP, maybe tossing in a freezing trap somewhere in the middle of that, and try to kill them with DPS. I'm not sure if landmine traps still stack, but you could also use that (I'll test it out and post here later after I'm done testing.. I was told that it was removed. Aside from that... You really just have to keep their SP low and kill them. Priests have very high SP regen, so even after being hit by two shockwaves, give them a second and they'll be able to heal again.. It's really tough. You'll want to wear angeling or water ol against them.
Sniper vs Paladin - Same deal as above, you won't be able to kill a good one. Wear GR and Deviling, ankle snare and get out of their range, and try to kill them. I don't really know what else to say, you really can't win this fight.. Even against Paladins who don't know what they're doing, really. Defender + Angeling + Noxius + Toad + Valk Helm lowers your arrow damage so much, it's useless.
Sniper vs Scholar - Scholars tend to hide in their wall of fog, but luckily they're only able to place two at a time. I haven't really seen this matchup for a long time, so I'm not too sure what to say about this one. You'll most likely want a GTB swap with you, in case they start waterballing you or things start to seem too icky. You can tell if they tried to waterball you with GTB on if some of their deluge disappears but nothing happens. I guess the best bet here is using ankle snare and shooting them from afar, or just keeping out of their heaven's drive/waterball range and DPSing them.
Sniper vs Clown/Gypsy - I really don't know about this matchup, I've never really seen it or been in it. Gypsy's belmont is fire but they also have asperiso so you'll be dealing with Fire/Holy melee and 
? arrow vulcans. I'm pretty sure you can out DPS them, though... Ankle snare + getting out of their range and DPSing them as always seems to work well. For clowns, I'd assume you'd use wind marc and just try to out DPS them.
Sniper vs Bio - Deviling, ghostring, and stay FARRRRR away from them. They can easily break your bow, so maybe place ankle snares all over when running away and hope they run into one. Or just run and gun them, using charge arrow or pha...whatever the other one is respectively.
Sniper vs Champion - First of all, Ankle Snare does nothing against them. Skid traps can push them out of Pneuma but it's easy enough for them to Pneuma again. If you have enough flee, you can laugh as their FO misses you and does like 25 damage... If you're running no flee, plant a safety wall next to the pneuma. Go into the pneuma as needed, and when he attempts to melee you, just step into the pneuma.. Again, it's a pretty hard matchup. Very hard. Freezing traps do you wonders, if you forsee an asura use safety wall + water OL, they should kill themselves. General rule is to wear your water OL when they're far from you, and wear your GR when they're right next to you and you have no safety wall on you. I don't really know about this matchup, it's pretty hard to beat a good champion as a Sniper.
By posting this I'm not saying I'm a great Sniper or anything, either, so I'm sure there are others that can contribute more or fix anything I may have said wrong. However, I do think that's the gist of it. Snipers aren't really a PvP class. By the way, Razerman makes a good point - Potless PvP is like your home. Shockwave traps ruin Champions there, as well as others like LKs and maybe even Paladins.
I agree with most of that but there are a few things that would play out a bit differently.
For Lks: you have to lure them out of range of people in general since (when snared) they tend to use other people for their charge attack if you're out of range.
For caster classes: Sniper range > theirs for general dps so all you really have to do is run reductions based on the classes. Against a scholar run Water armor and Hode for reductions and use charge arrow to keep them out of range. Fog is an issue but (like previously stated) they can only have 2 down at a time. People don't generally realize this but arrow shower is a ground targeting skill so it actually can be used to get a scholar out of fog instead of trying to spam charge/phantasm arrow and missing due to fog.
HW don't have the luxury of fog so just use a wind marc with a wind garment and possibly a maya swap. Strategy for fighting them is the same.
Sniper vs sniper: is sort of pointless (in my opinion) but if you do so just make sure you run vit build (vit always wins against flee) and carry these arrows. Shadow, Silver, and Immaterial. Most people always think to use angeling in a sniper duel so wear the shadow arrows first. If the hits aren't connecting swap to silver. Other than that it's a guessing game between the two of you.
Sniper vs Sinx: Hotkey toad and your Artemis. Most dagger sinx always use soul breaker first so you use the shield do reduce that damage, sharpshoot them once for burst damage, and then dps while swapping between agriope and gr armors as needed.
Against a TF sinx: just keep sw up, charge arrow once and dps.
Against a clown or a gypsy: you can easily keep them crit locked out of range.
Against a bio: This fight tends to be a bit weird. I start out with gr/devi/toad shield on and walk around til I find them. Swap to artemis when comfortable and charge arrow them twice so they aren't in ad range and start to dps them. Once they're locked out of range, swap to Evil Druid armor since many of these tend to resort to status armor + potion pitcher spam. If they close the gap between you just lay a few snares (after swapping to gr and toad so your bow doesn't get broken) and get out of range again. The fight should be over fairly quickly.
Sniper against a good Pally/Champ/HP is possible but extremely hard so I don't recommend fighting these right away.
