I'm looking to attend SFAS. Any advice on preparing and what the community is looking for?

It's helpful to be in good shape, though not really necessary. You'd be surprised the amount of people who make it through and are less fit than your average paratrooper. But being fit certainly makes selection a bit more bearable.
Physically, just be capable of carrying lots of weight at a consistent pace.
The best advice that someone gave me was, "Be the last to sit down, and the first to get up. Double check and retie the knots. Be an asset to the team." It worked for me.

I would make sure you're pursuing it for the right purpose and that you have a realistic idea of what an SF NCO does. It's not shooting people in the face, and it's not being a Network Ninja as an 18E. When I was a Career Counselor in SF Group, the most common reason guys told me they were leaving the Army was that SF was not what they were led to believe it was. As opposed to shooting bad guys in the face, they were doing training exercises with foreign allies most of the time. You will not become an expert in all things signal as an 18E; SF Command has a large detachment of signal support MOSs at each battalion, group, and an entire battalion of special operations signal personnel with numerous detachments across the world.
Finally, you might not be offered 18E. Whether it's your scores or their need, you may be offered something else. I was already a medic when I was selected. I attended with the express intent of becoming an 18D. All of my scores were very high, but I was given 18E instead. You are at the need of the Regiment. The name may say Special, but there are 24,000 special forces CMF18 in the Army and they will fill your slot with someone else who wants it of you don't accept what they offer.

My advice would be research the lifestyle first because that will determine whether or not you enjoy it. Better yet, go to Airborne School and reenlist for an assignment at a group so you can see first hand. Trust me, it will benefit you to have some regular army NCO time under your belt prior to switching.

All I can say is thank God that I was in before the SFAS! I don't know if I could have done it! My best advice is to be in the best shape you can be in! You need to condition yourself by lots of long distance running and you will need to condition yourself to "rucking". Use the same type of rucksack that you will be using and begin to build yourself up. Start with 25 pounds and begin working yourself up to about 75 pounds. Begin working on your distance and speed. Try to stay at under a 12 minute mile. Work on your rucking technique, use your hips to increase your stride. But most of all, be a useful member of a TEAM! Help those who are struggling. It's not about you, it's about them! You will mostly need to keep up a positive mental attitude, you CAN work through the pain! Lots of others have been through this and passed, and YOU can too!