Try to land an Inkstriike somewhere near your teammate, or at the edge between the turf you inked and the opponent's turf. This allows your teammate to advance and hopefully splat some enemies.
Inkstrike is also a nice weapon to use in Ranked. It can instanty neutralise an enemy zone in Splat Zones, either splat or forces opponents to get off the tower in Tower Control, can instantly break the Shield of a Rainmaker in Rainmaker.
It's also useful to get your opponents off a certain spot that'll make your team hard to ink turf around in Turf War mode, especially when you're playing in Blackbelly Skatepark, where there's that Tower where if an Inkling can successfully climb up the tower it's easy to control the battle and most likely bring Victory.
If you get your Inkstrike ready in the last few seconds try landing it in an area completely covered in enemy ink. Your opponents will not be able to patch it up, and if you launch it in the last second, even when the time is up the game will still allow the Inkstrike to land before it calculates the marks.
But if you do so when there's plenty of time, it'll only take a few seconds to patch it up.
When you see or hear an Inkstrike incoming, try to leave immediately. Don't get yourself cornered. Inkstrikes hardly ever ink walls, so if you're cornered try ink the walls and climb on one. You'll still take damage but most of the time it's better than staying on the ground and most players aren't stupid enough to land an Inkstrike on walls.
During Singleplayer, whenever you face an Octostriker, Cap'n will advice you to constantly move around so the Octostriker can hardly aim you. But this does not apply in Multi player. Inkstrikes are for inking turf but not
If you have recon ability and a weapon with an Inkstrike special, you can fight like an Octostriker if you want. Super Jump back to your spawn point and you'll be able to recon. Then unleash you special on them.
Hope these tips are useful! Keep cool and stay fresh!