Goal setting is an important step on any journey. Setting goals puts you on the path you choose to walk. It is not enough to just state your goal or goals.
They key word for goal setting is: SMART.
Specific - In order for goals to be effective, the goal needs to be detailed. A short and concise sentence will work for this purpose. Make sure to avoid general statements like "I want to be thin." Instead, start your goal with something like "I want to lose x pounds in y time." This might change once you move forward on your journey; you can always readjust the goal.
Measurable - The goal needs to be measurable. It is not enough to say "I will lose weight" or "I will start a business", you need to quantify you goal, this helps in making the goal more specific. In the case of losing weight, how much do you want to lose?
Attainable - Your goal also needs to be realistic. You cannot expect to lose 20 lbs in 2 weeks, your goal needs to be attainable. Losing 20 pounds in 2 weeks isn't realistic for most people, and even if it happens it is most likely due to water loss. Do your research to make sure your goal is attainable and reasonable for what you are trying to achieve.
Relevant - Although it seems obvious, your goal needs to be relevant to what you are trying to accomplish. This is a good time to figure out the "why" behind losing weight, if that is your goal .
Time bound - And last but not least, your goal needs to have a time frame. Don't leave an open loop, even if you need to extend the time frame later, you still can, but you need to set a reasonable time frame to attain your goal.
Once you start working towards your goal, things can change and you might need to adjust your goal or some parts of it, but start with a stated goal and always make sure your goals are SMART.
Here's a series of videos from the father of life coaching Tony Robbins: https://www.youtube.com/watch?v=7H2uNIChYtQ