I don't claim to be an expert at this, but if you are looking for some concrete ideas of various means of communication, I will gladly share those that my wife and I have tried.
Talk in person. This is the most obvious way to talk to your builder. Of course if your builder commits to doing more than he ever intends to do, you may simply find this frustrating.
Email. This is often the easiest way to communicate specific issues in a way that won't get lost in the shuffle. If you send a list of issues to your builder, he or she can continue to refer to those while the work is being done to make sure that nothing is forgotten. Note that this doesn't work for all builders. Our builder doesn't reply to emails at all.
Voice mail. This is a great way to get your builder's attention. They don't have to log in to a computer to find out what you have said. If you use voice mail you are leveraging one of the builder's day to day tools, and are sure to get his attention. Unless he ignores it completely like our builder does.
Notes in a mailbox. This combines the pluses of both email and voice mail. Your builder probably visits his mailbox about once per day, so this should definitely get his attention. In some cases the builder doesn't respond though.
And finally, if all else fails as it has for me, it can sometimes help to get creative.
