You have to be restrained and wait to use your rush until they're as close as they get, then rush a couple ships all at once towards the centre of their fleet/their biggest ship and board it as many times as possible.
Other methods are cheap escorts with the tentacles, but instead of using the one that eats troops, use the use which pulls the enemy closer.
The sporemine cloud is good as it slows down enemies and you can hide in it.
Stealth you ships as much as possible so the have to get close to spot you again.
And ram if possible.
@brohanbroski Since my game has that annoying bug where i cant create new fleets because my pc fill freeze to death i usually use the preset fleets, although it let me create one once which is the one i use the most i dont remember well but i can upload a better description later
It has 2 tentacle hiveships
one baattlecruiser with claws and the rest were normal cruisers with tentables i think.