Goals should be SMART
Specific – Well defined and clear to anyone who has a basic knowledge of the project.
Measurable – Know if the goal is obtainable and how far away completion is.
Attainable – Realistic and achievable.
Relevant – Based on overall project aims.
Time Based – Enough time to achieve, but not too much to adversely affect project performance.
When producing monthly or quarterly goals, I find it helps to have an overall medium term objective for a specific time period such as a year which is clear and simple.
Based on this the shorter terms goals can be established and as progress is made they can be refined or adjusted.