What to do to be prepared for SFAS?

Step 1, If you don't already know, figure out how many days a week you can run and lift without causing an overuse injury, or dropping points on the APFT. For some that's 4-5, for some it's 7.
Step 2. Work out that many days a week, 2 of those run days should be replaced by six mile rucks with 45lbs as fast as you can go, (not back to back days), with both pairs of boots you will take to SFAS.
Step 3. Keep doing that until those two 6mi rucks can be run the whole way, or at least as close to 60 min as you can get.
Step 4. Keep lifting, squats and shrugs are what will pay off with the tick on your back for 21 days.
This workout should be solid for the six weeks prior to SFAS.
Step 5. Taper off the last 7 days before you go.

This is not a year around workout.
If you aren't preparing for a selection, you don't need to ruck more than once a week or two weeks.

I made a sand baby about 70 pounds, tossed that in an ALICE pack and wore that around all day every day for about three months. Worked out really well, actually. I didn't even do any ruck marches or PT for about a month before I left

Two words —-> Land Navigation (LandNav). Back in the pre-SFAS day (and regardless of today’s Q *Phase* numerology du jour) upon arrival @ MacKall we were told 1/2 of you will be gone in two weeks. True to form about 14 days later about 50% (regardless of branch, enlisted, officer, AD, Guard or Reserve) were trucked back to Bragg for out processing. For sure being in great shape, a *ruck*-stud, team player/leader, able to think/react on your feet = a given; but, if you cant find your way from Point A to B (and beyond) in the dark (and rain) —> game over.