Did you have a weakness (that you realized) or were there areas you where you didn't know the answers in the tech portion? You don't have to know everything, but you should strive to look like you learned everything you could. You should absolutely know your current aircraft inside & out.

Make sure you know whatever you missed the first time, but don't focus on it to the exclusion of the rest of the areas they emphasize, ie jet theory, weather, FARs, Jepps, Systems, etc.

I agree with the others - attitude and personality are huge. But when I got hired, the Captain also told me in the debrief - "we're looking to see if you can make it through ground school. It amazes me how many people show up without preparing enough." Keep that in mind.

Study until you can't study anymore and show up with your best attitude. You've already got a leg up because you know what's coming.

Good luck! If I can help you at all, feel free to PM me.