"Inattention obscures, attention clarifies." ~ Sri Nisargadatta Maharaj
Project management, Drupal development, Customer support.
All of these passengers ride on top of the tiger named: 'Attention to Detail'.
Simplicity--the art of maximizing the amount of work not done--is essential. - Agile Manifesto
The beginning - The Agile Manifesto
An Agile Approach to Estimating and Planning: Chapter 3 - An Agile Approach
An estimate is just that - an intelligent guess based on a problem description provided by you and some investigation provided by me. The more accurate your problem description the more 'on target' will be my investigation and thus the more easy it will be to make the estimation.