Underwater battles - need tips

So first off - I dislike underwater battles. I find them tedious.

That said, I recognize underwater battles as a necessary form of evil within this game. So this brings me to my current predicament.

Green Plesioth (G-Rank)

I mainly use LS, with the very occasional hammer and lance. I mainly only use Hammers when fighting Raths, although in the end I decided it was far more efficient to stick to LS because of how hard it is to aim for their head. And I only use lances when fighting Diablos, Uragaan, Barroth, and Jhen Mohran, I'm not very good at lances either.

So my question to the community is what kind of fighting style should I employ for underwater battles with a long sword? Not just particularly against Green Plesioth, but against Goldbeard Ceadeus too for example. My current problems include not being able to find a good enough opening to hit a monster, only being able to hit them once before they move around or I'm forced to dodge (no stunning power), and never being able to get a first level Spirit Blade.

I am really not looking forward to G-Rank Lagiacrus and Abyssal Lagiacrus simply because of the underwater battles. I probably had more fun hunting Ivory Lagiacrus than the regular one. I have a LS for every element, and my strongest LS at the moment is an upgraded Jho LS.

Thanks for any help.

Get full spirit, press R then A, then fade slash to the left, right, or backwards. If you're having trouble underwater, you'd want to attack rather than try getting red spirit.

If you visualize the monster's head as 12 on a clock, try to stay at say, the 10, or 2, etc.
This angle is often a good point to attack monsters, notably Plesioth, and not be directly in range of attack. Underwater has the benefit of also adding the vertical element, allowing you more room to avoid attacks by going upwards. Combining the provided position and upward dodges can remove a lot of instances when sweeping attacks, like the Plesioth tail swipe, would've hit you.
The same can generally be applied to Lagiacrus. His hipcheck can be avoided by going upwards or downwards from it, and that's his worst attack due to it's damage and frequency. Otherwise keeping at his sides, and then using break chances to stun it should provide opportunities to pull of a spirit combo.
And Ceadeus really isn't worth a strategy. He's such a large target that just staying behind his head at water blasts is the only advice really needed.

Ok I will give all this a shot, thanks guys.