Hey mate ,
If your using soft plastics give the doyble uni knot a go , easy to start off with,
Another good knot is the allbright not. Theres a heap of different ones out there . Just make sure tyey are nice and neat
If your braid to leader knot isnt neat or trimmed you can sometimes have dramas with it going through your guides poorly. Itll cut down your casting distance a bit
Sqidwards length of leader is pretty spot on
however be carfull when your length of leader is so long that the knot winds onto your spool before you cast, if the knots untidy it Can tear off braid when you cast giving you a bad tangle
Thats what happened to me anyway
Cheers
Morgs