I'm putting people's strategy advices in the OP and crediting them. Check it out! http://gamrconnect.vgchartz.com/post.php?id=7301435

I'm also going to put an index on top so people can use Ctrl + F to find it. 

I'm also linking the question and answer post I made above your post to the OP as well. Here's what it looks like so far! http://gamrconnect.vgchartz.com/post.php?id=7318465

After playing for a bit I've found a strategy that I usually stick to when playing Splattershot and Splattershot Jr. I usually stick with jumping, spraying in front of me, then diving back into the ink and repeat it. I find it useful at the beginning of matches since I can cover decent ground while still maintaining decent speed. Same thing with combat, though I usually use jumps to strafe more often in those situations.

Whenever I try to push into enemy territory (like, say, on Urchin's Underpass) I chuck some Splat grenades or whatever sub-weapon I have on hand to make crossing into those areas a little safer. I'm still trying to figure out more stage dependent strategies but I might need more time to figure those out.

It sounds like a odd strategy I've seen people jumping. Constantly jumping. Since most people splatter the ground, if you're in the air you will most likely take less damage. Jump while shaking the Splat Roller will give you longer range and spreads your ink out more.

Use the Aerospace RG. I get over 1300 points consistently (after winner bonus) and just got a 25 flag "So Hawt" streak. This gun is insane.