The following instructions assume that you are about to choose a program (lab or project) and/or a quiz to work on.
No matter whether you are wanting to work on a lab, project, or quiz, your primary concern should always be: "What can I learn from this assignment?" When you are picking out an assignment to work on, look over the topic list that the assignment is supposed to cover. This can be found in the original table for quizzes and labs or in the 'Topical Information' section of any type of assignment. Think about what topics (that we've covered) that you are still unsure about. By working on an assignment about that topic, you can build your understanding of it. You don't learn a language by simply reading about it or watching others use it. You have to dig right in there and use it yourself!
If you are sure you understand a topic, you can still do assignments about it, but wait until that last week of the portfolio period and see if you haven't got enough items/levels or not. If you really understand it, you shouldn't have much trouble whipping out a solution in a week.