The mechanics of creating a budget are well-known, and, while not very enjoyable for many people, not hard to complete. The difficulty lies in implementing and sticking to your budget. You can greatly increase your chance of sticking with your budget if you give careful thought to the CHANGES that need to be made to get from your old budget (starting position) and the new budget you hope to implement. Each change should be classified as either a ELIMINATION or a SUBSTITUTION.
An elimination is when you have to totally get rid of a particular spending behaviour - for example, quitting smoking or cutting up your credit card. These changes are very hard, and should only be done if absolutely necessary. A lot of changes SHOULD be classified as a substitution - for example, drinking filtered tap water and tea rather than softdrinks and Starbucks. These are usually much easier to implement as you are not having to eliminate a behaviour pattern 'cold turkey', but are still able to follow your normal routine with minor changes. Generally, after a week of substitution it will become a habit and can be followed without any further effort of will needed.
Many people make the mistake of classifying intended changes as an elimination when they should be aiming for a substitution instead. For example, if you wish to save on entertainment costs, it is far better to substitute your cable TV subscription with borrowing DVDs and books from your local library, substituting gym membership with lunchtime walks and so on. Trying to eliminate spending without introducing a suitable alterative will leave you in a permanent state of "deprivation" and you are more likely to fall back into old spending habits.