What kind of neckline and what is the st patt (ribbing?)? One option is to use a larger ndl. Or, on standard chain, pull the worked loop up a bit longer before BO. You can also do a YO BO which allows you to input YOs, where you deem necessary, to thereby add sts to the BO (making it longer, looser). Tubular and sewn BO can both be adjusted in terms of their 'looseness.' (Tubular also looks really neck on a crewneck.) Keep in mind you don't want it to look TOO loose...to the point of being saggy or unable to retain its elasticity once over the head.
Keeping to the knitting basics