basically, how do you get the full rotation and keep the board underneath you, cos i get pretty good 180's and if i go for it can get 270's lol but i can never get the full 360.. is there like a trick to it or is it just down to perservance?

I expect it to be just constant practise.

pivot the shit out of the landing

aim for your back trucks and pivort the rest.

The full rotation will come after soing them like that alot.

I learnt Switch FS one's on a slightly slippy surface, enableing me to revert the last 90 or so making them not too hard. I find that wrapping your body up before hand to prepare (bring your arms back and swing them to get the motion) helps with getting the spin too.

Practice

Oddly my switch f/s 360's are far better than my regular ones.

With switch ones, I can somehow get my body to rotate fully making them not so hard, whereas regular ones, my body only wants to turn 180!