birds nest braid

im just back from an evening spinning for sea trout. really enjoyed it even though i didnt catch any (despite a good few showing - they were just out of reach.. ) but i did catch around 20 pollack averaging a pound...
however, i was fishing with some new 20lb braid but i kept getting birds-nests up the line during my casting!!!
it was driving me crazy!! why is this happening???
any help/advice received gratefully!

its a decent rod and reel and i think that there isnt anything wrong with my casting so i dont understand it. most of the time it was a nice smooth cast, then the other times it was just a mess.

First thought to mind is there is too much line on the spool.
There are other posts up about the same problem.
A search might find them

Updated: from a "search" using the word "braid" here is one of the many posts viewtopic.php?f=1&t=35882

cheers donal, thanks.
indeed, i got the questions answered elsewhere on the forum!
too much line on the reel was a starting problem anyway, but all good now i hope