Read your assignment. Underline and highlight key points of the material. Strong notes depend on a strong understanding of what you've just read.
Reflect on the assignment. Identify the main points from the reading and find an overarching theme. Readings are often assigned by chapter (depending on the subject), which means they only pertain to a few ideas at one time.
Rephrase the the things you have read in your own words. Organize your thoughts in a manner you're able to easily follow.
Review your notes. Go over areas you found particularly important or think might be touched on heavily in class. Reread the reading assignment and expand on areas you find light on pertinent information.