don't feel pressured into advancing early. you're not using an assault weapon that can take on multiple enemies at once. even one enemy is trouble if they can get in range of you.
don't jump down into an un-secure area unless you have NO CHOICE or a kraken or something. other weapons can just hop down from above and get kills. snipers don't do that. same goes for popping up onto a ledge; don't hop up unless the coast is clear or someone below you is trying to kill you.
don't stay in the same perch the whole game. generally be nearby your team, but if you secure a nice perch, the enemy team will figure out where you are and they will remember (sometimes your team's stability relies on you, and the enemy team knowing where you are and plotting your downfall can reverse the tides of the entire match).
always have an escape. some friendly ink trailing back a ways, curling around to safety. if an enemy gets too close, this is your escape. don't be afraid to superjump (if you can manage it in time).
don't be afraid to duck into the ink and run away mid-charge if someone gets uncomfortably close. it doesn't even have to be THAT close. you retreating to better spacing is better than you getting killed because the dude got just close enough and pulled out a bubbler or something.
watch your teammates's backs. you like having an escape at all times. if you don't have a clear shot of an enemy but you see your teammates engaged, ink an escape route behind them.
half-charged shots are really useful. if your enemy has some damage or is already standing in your ink, you don't have to charge all the way to snag the KO. most skilled squids are used to the timing of your OHKO, so mixing in half-charged shots when you know they'll still get the splat will throw a big wrench in their dodging maneuvers.
ink over obstacles when enemies are hiding behind them. this is a way to incapacitate them and make them an easy kill for teammates (or at least to scare/upset them).