Trying to get better at sniping, could use some advice

My advice would be probably different to everyone elses so er... just listen to everyone else

I find it easiest with the female quarian infiltrator and the Widow... shes pretty similar to the human but she has more shields... the Widow is just beautiful and I find it easiest to aim for some reason

Id say dont shoot quickly, take your time with your shots and youll eventually get better

On the female quarian infiltrator, I always miss out on sabotage (I also miss out siege pulse on the geth Juggernaut so er yeah might not be the best )

Learn the "pattern"... I know I can kill a Nemesis with a headshot, a ravager in 2 shots... just learn the pattern of how you can kill things... I see lots of patterns in multiplayer, and like... when it comes to sniping I kinda have different patterns for different enemies, I might be weird when it comes to this and its hard to explain but my multiplayer is just me with my indescribable patterns... when I play with someone ive never played with before the pattern is all wrong and a mess... anyway yeah patterns are important

I find collectors the worst enemy to snipe against, lots of things to throw off your aim and the possessed enemies are bad and take more to kill... I find Cerberus and Reapers to be the best

Also another bit of advice from me: play Skyrim... the biggest improvement with my sniping was with playing skyrim rather than mass effect for some reason, it helped me aim better and shoot faster/more accurately with my time using a bow

Oh and apparently phasic ammo is better on 1 shot snipers than armor piercing but in my opinion armor piercing and drill ammo are better for some reason

I'm worse with Drell than with snipers 

I never could figure drell out. Constantly getting killed when I play them, they are so squishy. I have the same problem with vorcha, they are dead before health regen can kick in.

Think of the drell like a phantom. They're a huge pain in the ass to kill when they're moving. Move laterally where the enemy has a harder time shooting you. You can strafe through a whole open field of enemies without taking damage a lot. If you just can't avoid getting hit, dodge. You get damage reduction which will save your ass. With all that and the damage output you can manage you shouldn't be taking that much damage. Reave will give additional DR, cloak should drop the aggro you're taking with the stagger of recon mine as well helping you, and biotic charge refreshing shields on the vanguard. Drells aren't glass cannons; they're just fucking cannons if they're played properly.

Weeell, the git gud advice here is Dont Get Shot!
It should be cover that keeps you safe not shields.
The higher the difficulty the less difference the amount of shields make anyway, at least comparing the humanoid characters.
Point is, use cover and be a sneaky bastard, you are a sniper.
Put on a geth scanner, throw out your recon mine, shoot them through cover (add piercing mods), you don't need to duel them.
When they rush you the drell can move to the next cover like nobody else.
Additionally you are an infiltrator, every time you cloak (ideally in cover) you throw agro off you, enemies will start to look for your unlucky teammates.
You can start learning Drell and Sniping both with the DAI.