Opening of game don't ink the base meticulously, instead get to the middle third of the map and secure the area (maybe get some splats if you are able to get to an advantageous position like the centre of skatepark).
Once you get splatted and respawn you can do a pass of the base while you return to the front lines. It also gives you something to do if in the last few seconds if you are just respawning and can't super jump anyplace.
Anytime during the battle you can super jump to any team mate or the spawn, use it to provide quick backup to team mates or protect your base (in turf wars). If you don't have ninja jump, don't go for risky jumps, sometimes it's better just to swim and flank.
The arrow that sometimes appears on your screen with your team mate's name is them tapping on your icon on the gamepad signalling that they're probably going to super jump to you as soon as they respawn. To prevent them getting jump camped back off to a reasonably safe position. This applies if they are mid jump to, try to at least watch their jump location a bit before you head elsewhere.
Some tips to play against Krakons include destroying their beakons (you can see them on your gamepad map) so that they don't keep jumping behind your team, walking backwards and shooting like they were a pyro, and swimming away from the Krakon as it only swims at 80% of normal squid speed and has a moderate turn circle. Apparently you can also jump over rollers rolling, but this should pretty much be a last resort.
If you are playing with a roller know that you are mainly a support role, like chargers. You can get splats sure, but realise that there are better things to do in turf wars than ninja camping to get the jump on someone.
In turf wars, inking walls does not count for the percentage covered at the end of the game and it charges your special at a reduced rate. This doesn't mean that they are completely useless however. Painted walls don't appear on the map so you can approach enemies without them possibly realising you are coming. It also means you can hide in walls since people don't really paint walls (since they don't count) and jump out and splat everyone, ink resistance is useful here. In relation to this, you can pretty much track the entire enemy team's movement by just watching the map and the paint trails.
Jumping does not increase the distance your gun fires, but it can be of varying use in a firefight.
Main defence up past the first one are useless, the first defence up lets you survive an additional .52 gal shot (from 2 to 3) assuming you don't take any other damage. One attack up upgrade completely negates any defence upgrades, but other than that does nothing since the shots to splat does not decrease.
In splat zones please contest the actual zone, and only charge special in areas close to it, don't ink the bottom of saltspray rig for example.
Know the range of your weapon versus the range of your opponent weapons. If you are using something like the .96, abuse the fact you outrange any other shooter and 2 shot them before they even have the chance to lay any ink near you. Similarly, if you are using a weapon with less range don't try to blindly run into someone with something that outranges you or you will just be throwing away your life.
You can easily look behind you by tilting the control stick so your character turns around and pressing Y to center the camera, this is much easier than swinging the gamepad around.
If you are using the Bubbler, you can pass the shield onto team mates by bumping into them when you have the shield.
Also look up, squids, beakons, sprinklers - all manner of things could be hidden.