While I did not intern with them, I know the ones that were extended a full time offer are the ones who created visibility for themselves. You can be the best at your job, but if every person in your floor doesnt know that, then it's not very useful. This may sound crude, but like I said, everyone in there is smart, so you have to stand out and either network with the right people or make sure all your accomplishments are being noticed by your managers (and potential managers if you wish to work for a different team).
Outperform your peers. Work harder than others. If you know something, share it, if you don’t know something learn it. Communicate, be respectful, and be known. If people know who you are and they respect your work, then you have a good shot of getting a full-time offer. There are no guarantees of getting a full-time offer, since the quotas for how many people get hired come from higher up. However, if they are hiring, you want to be on top of the list, so it helps to know and have a good reputation with different team managers, but most importantly be in good standing with your direct supervisor and team manager.