Wow, I didn't know that pride could help me win games! Guess I'll drop my Enperries and pick up a Flingza Roller! A full Cold-Blooded build will surely give me enough pride to help carry me to X-rank!
I'll have you know that the Flingza is the work of God himself.
As for the thread, here are three general tips :
1: Know what your weapon is supposed to do. Check out
this thread about player/weapon archetypes and tips on how to fill the role, but for now, the long and short of it is that Dapples are Attackers/Controllers, so you need to be attacking enemies, and inking the way for the Rainmaker, making sure nobody sneaks up on them, etc.
2: Know whether your job is being done already. Attacker/Controllers are common weapons, and they tend to be the most commonly played too. If a teammate already has a weapon built to kill and turf, make sure that either you or they are the one to pick up the Rainmaker, and try to fill a different role (as long as you're at least a little suited for it; e.g. don't Carry as an E-Liter unless you absolutely have to).
3: Know what you're doing wrong. Accept that you're doing something wrong. If you weren't, you'd be ranking up - your teammates and enemies have the same average skill levels, so if you're losing consistently it's probably caused by your 25% of the team being below that average (assuming your team isn't made entirely of Attacker/Controllers). Try to figure out if you're losing easy 1v1s (practice more with the weapon), getting caught unawares (try to position yourself more in line with the weapon's strengths), etc.
As for what you're doing wrong specifically... Sounds like you're not thinking of the Rainmaker carrier enough.
You seem to be fulfilling your roles, but doing them in the wrong places. Sticking closer to the Rainmaker (but still ahead of them) can help to convey that the way is safe to travel - you're there and not being killed after all. If there's a huge gap between you and the Rainmaker, that's a huge area where any number of (well, up to four) enemies could be lurking.
Pay attention to the direction that the Rainmaker is shooting - usually that's the direction that they want to travel. Instead of trying to pull them to a different path, let them decide where to go and lead the way.
Make a show of defeating any enemy that gets close and then saying "This way!" - inexperienced players will often ignore this prompt because it's coming from offscreen, but if you're right ahead of them and are good enough to kill enemies, then obviously you can be trusted. Remember that "Booyah!" and "This way!" are easy to mix up though.
Stop in front of someone, then go into Squid/Octo form twice quickly. Through the mystical powers of non-verbal language, this conveys that you're confident, and makes people want to follow you. I still don't understand how, but don't look a gift horse in the mouth.
Now a few tips for the other modes:
Splat Zones caters to longer-ranged weapons, because they aren't forced to be on the Zone in order to paint it. Dapples aren't particularly effective here, but if you insist on using them, try attacking enemies behind the objective, and let your teammates mindlessly take the Zones for you.
Tower Control is great for Attacker/Controllers, but you need to control the area around the Tower rather than the Tower itself. Try not to waste time actually on the Tower unless nobody else is stepping on it. Remember that enemies can jump down onto the Tower from above, so try to control any high-up areas near the objective.
Clam Blitz is a weird one. Ink as much as possible (only clams on your ink appear on the map), collect clams, and remember that you can throw them at your teammates to get them up to 10. Try to occupy the middle-back of the map until you can find three groups, then quickly gather them and bring the Power Clam to the enemy basket. Remember that although you can be seen while holding the Power Clam, you can also throw it away to sneak up on nearby enemies, then pick it back up. It's a risk to do though, because if you die it'll already be despawning.