Which maps are you in need of help? What weapon are you using? What is your playstyle?
Generally speaking there are two schools of thought when it comes to Turf Wars:
1) Ink the base first then head to mid to engage the enemy
2) Charge to mid first and take it. Keep enemies out. Ink the base on respawn.
Personally, I think inking the base is the better strategy for several of reasons:
1) You charge your special quickly, having it ready by the time you get to mid.
2) You have more room to maneuver if you lose the first push to mid. I've had times where I arrived at mid after my team lost the first push and had to retreat, but didn't have options because large parts of the base weren't inked.
3) If you charge to mid by yourself the likelihood of you being in a bad numbers situation is high. I've seen it over and over again on Port Mackerel. The enemy rushes to our base, they leave their teammates behind, and get splatted because there are 3 or more of us still there. Unless you are a ridiculous player, charging in by yourself is a bad idea.
4) Ensuring that you have all your base covered can swing close games in your favor. I've seen it on both sides: one team is slightly better than the other, so they usually win mid but can't push to far in BUT they didn't cover their base. They keep rushing to mid to push in, but end up losing because large chunks of the base are uncovered.
5) Helps with travel routes to get back to mid faster. You should very rarely super jump - you will likely get splatted. So swimming is the preferred mode of transportation. If you have to ink parts of your base after respawn you are wasting precious seconds that your team needs you at mid. Also, if there is a route to mid that was left un-inked then you have to ink that on the way instead of just swimming.
*There are exceptions to this rule, but generally you want to ink the base upfront so you can engage the enemies easier*
So, that's my spiel about inking your base.
In terms of map strategies:
1) Recon each map before jumping in. Know the range on your weapon and where you can hit people. Know different routes you can take to mid. Be aware of any water hazards, moving parts, walls to climb, good flanking spots, and other ways to move around.
2) When playing, take note of routes other people take: do they always charge down the center? Do they try to flank? What patterns to people have?
3) Related to 1 and 2, what are some chokepoints that you need to control? How can you position yourself to protect those chokepoints. Examples:
- From the right sniper perch on Blackbelly you can shut down the entire right side. With a charger or jet squelcher you can hit approaching enemies as well as enemies on the central tower
- On Walleye, the left catwalk is a great place for enemies to drop down and flank, so keep an eye out for ink trails or enemies coming from THEIR catwalk (your right). Likewise the right ramp (your left) is a common place for enemies to push out, so keep an eye out there to stop flanks
- On Saltspray, the goal is basically to take the top AND the middle areas. You will win as long as you have these areas. This is actually a map where I tend to rush forward instead of inking the base because the top and middle are so important. Take the middle and defend it with all you've got. Call your teammates to you to help ink the top.
- On Moray towers, if they don't have a sniper you can ink the ramps first, or if there is someone already doing that you can rush to middle. If they DO have a sniper, you want to rush to mid as fast as possible and get on their ramp to deter the sniper. Watch the ramps and drop offs for people trying to flank.
Etc.etc.
EDIT: This video about angles/positioning is helpful, even if is not for Splatoon explicitly. Knowing these angles on each map is crucial. Recon and just noting people's patterns is a way to get good at angles.