I'm levelling an eng specc'd sniper. I dunno if this will help anyone, but a few things i found out about the hard way that made my life alot easier.
1. Make your sniper an armstech (i was arms, scavenger, investigation). Mainly doing this for levelling to make barrels for you and kaliyo. Make green barrels for your level, RE them for the blues (should only take 3-4 at most to get the blue) and keep an up-to-date blue barrel on both your rifles as you level.
2. Solo Black talon at your earliest convienece. I was soloing it around 8-12. You can get the orange trench coat to drop, an orange sniper rifle and a bunch of blues. I had my sniper and kaliyo all decked out by level 12. These low-level ornges will last until 50 if you replace the armor mods in them.
3. you should be able to get the orange pants and head during questing on Kaas. one of those is a quest reward, other is a fairly common drop.
4. Start pvping at 10 if thats your thing. I use Pvp to get commendations to buy gear at 20/40/50. If you pvp enough, you can keep your companion in pvp orange gear as well. Keep kaliyo in heavy gear obviously. 2-3 matches is usually enough to get decent orange/blue lvl 20 pvp gear.
5. replace armor mod in each piece of equipment every 2 levels, and mods as well (but armor takes priority). Always socket with blue level armoring mod you get an extra +10 ar on same level piece with a blue (or purplse if you can get it).
6. As an eng spec, i never start out with exp probe, as it pulls aggro. I usually start with ambush, then probe, snipe, etc. Always throwing grenades when off cooldown, using rifle/adrenline for energy management. Suppress fire is good for Aoe if mobs are packed together and other important skils on cd and you dont have SoS yet.
7. Create a 'dummy' char if you dont have a cyber tech. At lvl 10, you can pretty much max out cyber on him/her and keep your sniper/companion in up-to-date armor/mods/ship components. They can creat the higher armor mods (they just cannot use them until they get to that level). I would recommend: Cyber, scavenger/slicing. Slicking on this crafter is used to get money when you are playing your main sniper. (only send out on rich/bounty lockbox one lvl below your max slicking lvl, always a profit)
8. In PvE, even if your Eng spec, at low levels shoot to get ballistic damper in mm trees if you take too much dmg. This helps alot as well.
9. My rotations change based on the mob, lvl, etc. I generally cc a strong/elite mob, burn his croonies downthen take him out. Kaliyo needs alot of microanging at times too.
10. If your overwhelmed, run away to a decent distance, then hit Kaliyos' passive stance, she will warp to you, usually saving her *** if you time it right. Keep her in guard stance too. For some reason, she doesnt default to guard stance.
Keeping Kaliyo geared in orange pvp gear (and myself for that matter) with up-to-date armor mods and barrels makes a WORLD of difference in solo pve as sniper.