Never promise more than a 10% improvement – anything more could be embarrassing.
Always charge enough to make sure they take notice of what you're saying.
If what they are doing doesn't work, tell them to do something different.
The closer you are to finding the cause of a problem the less chance there is of resolving it.
The frequency of an event is in inverse proportion to its desirability.
If anything can go wrong, it will.
Nothing works first time - but this time it will be different.
Your clients are always more important to you than you will ever be to them.
Trust takes years to build, moments to lose.