I'm going to steal/paraphrase a lot of what JY says in the vid lessons. If you have access to those, I'd reccomend going over them again and reading the comments.

The most important thing to remember for weakening questions is that the correct answer

choice is always attacking the support that the premises give the conclusion. Usually this is done by negating an assumption made by the argument's author.

"All force users are powerful, and all jedi use the force. Thus, all jedi are powerful. Tom is not a jedi, thus he is not powerful."

What's the assumption here? That the only way to be powerful is to use the force, and that Tom is not another class of force user. A correct answer choice for a weakening question involving this argument would state something along the lines of "Tom is the leader of a political bloc in the Galactic Senate that holds a super-majority." or "Tom is the aprentice of Darth Sidious, a force user and Sith Master."

For the weaken EXCEPT questions, ignore the EXCEPT. Instead, treat it like a regular weakening question. You will find four answer choices that will weaken the argument, and one that does not. To reuse the above example, let's say that in addition to the two possible AC's, there's one that says "Tom is the nickname of Jabba the Hutt.", "Tom has beaten numerous Jedi Masters in fights, even though he can't use the force.", and "Tom is an acountant." That last one doesn't weaken the argument, it's just a statement about Tom's career choice, and as such would be the correct answer in a weaken EXCEPT question.

Hope that helps!

Something I feel should be mentioned is that you shouldn't forget the work you've done for previous answers. many times, that previous work will help you eliminate some of the answer choices for future questions. Not just in terms of inferences either; I'm currently working through the In/Out Game w/Sub Categories 2, and the last three questions (21-23) run straight together (the work you did to answer 21 provides the answer for 22, which helps eliminate three of the five answer choices for 23, with the last incorrect one being eliminated by looking at your master game board).