[About to start a Sniper, any tips for someone who is new to the class?]

Are we talking PvP or PvE? In PvE you'll have little trouble taking cover and staying in it and/or firing from it, in PvP sometimes there are problems.

 

One of the first things to do is hotkey your crouch to F (or whatever suits your needs) and take cover to shift+f (the default is reverse). This is because rolling into hard cover (green guy) may have you aggroing mobs or endign up where you don't really want to be, so your first choice should mostly be crouching. Rolling into hard cover has huge advantages, especially in PvE, since staying behind it (without gettin up to shoot) makes you immune to ranged attacks.

 

As a class you have three issues you need to take care of:

-lack of mobility

-squishiness

-not much AoE

-energy efficiency

 

Engineering tree helps with AoE, Lethality pretty much eliminates the mobility problem. Marksman is the most energy efficient (to the point that a careful marksman never runs dry). All three of them offer some form of help with protection (whether an extra layer of defense of better cd with personal shield).

[Opportunistic Vulturism: A Sniper's Guide to PVP]

I've had similar evolution in PvP playing sniper. Initially I was trying to kill targets with big openers and sustained DPS, but eventually I realized the first thing a sniper needs to learn is not who to shoot or how, but where to hide. Because if I'm detected and targeted, I'm going to die. Oh I can hold my own from time to time, it's not like I get steam-rolled by anyone who can click on me, but I can do my job much MUCH better if I am out of sight and out of mind. Most of the time I'll hide somewhere and won't start firing until other people have engaged my target first.