Write the categories down that you will use for the project. Some examples of categories are content, neatness, style, conventions, etc. The categories should align to match the project you are designing. Most rubrics have between four and six categories. These categories are the section you are grading the project on. The more specific criteria for each project goes into point leveled sections that are within each category.
Write the criteria needed for each category. List, very specifically, the elements that the students need to include in each category in the top level. For example, if the category is conventions your rubric might state that there are less three grammatical errors and no spelling errors. The more specific you are in the criteria needed for the top level these easier the rubric will be to use when you are actually grading.
Write the criteria for each of the lower levels making the elements slightly easier as you go down. Most rubrics have at least four levels, four being the highest and one being the lowest. For example, if your category is still conventions, but your level is three your rubric might state that there are three to six grammatical errors and less than three spellings. If your level is two, your rubric might state six to nine grammatical errors and three-six spelling errors. If your level is one, your rubric might state more than nine grammatical errors and more than six spelling errors.