Firstly, May I ask what essay are you doing for your SAC: Context, Text response or Language Analysis?
For Language Analysis, you should fill them in with the effects of a particular technique. Explain the effects in detail, don't just write a summary of it.
Text Response: For every paragraph, have 2 - 3 examples that relates to you topic sentences, and explain how they relate.
Context: Very similar to what I said with text response, except that you need to draw from a range of resources other than the texts you are studying for this area of study.
Overall, do not focus on the quantity (which is what the word limit is), but on the quality of the essay. More does not always mean better, and even short essays can get high marks if their quality is good. Conversely, a long, bad essay is not likely give you any advantages.