It's not hard. I did like 2, 3 mile ruck-runs before selection and that was it lol.. if anything just toughen up your feet and get your shoulders used to hurting.. only hard part is team week that sucks dick
edit: basically if you're already athletic and do your own thing to keep in shape.. you'll be fine.. too many fools show up there can't really even do much physical **** as it is.. then it just gets to their head and that's when they quit
edit: well I guess when I think about it.. get your mind right and 'in the moment'.. don't think about **** 'back home' or whatever.. too many guys had problems thinking about **** outside of the task at hand and ended up quitting.. you'll realize this when you get there.. you'll realize "damn wtf these *****es doing here"
edit: What's your MOS? If you're infantry or cav or w/e you'll be good.. even though what we do isn't really 'hard'.. it's a lot harder than most the pogue **** and you'll see that when you get there with a bunch of pogues *****ing about some **** that they 'had to do' back at their unit one day and be liek "wtf we do that **** all the time" or w/e.. Also.. know the basics of land-nav.. just the basics if fine. you'll be brought up to speed when you get there.. PM me i'll send you an 'outline' that I sent to my bud awhile back right after I got back.. pretty detailed
edit again: in the end a lot of people end up talking it up more than it actually is.. at 'least that's my opinion.. lots of people don't want to make their buddies think it wasn't as hard as they originally thought/everyone else in the army believes it to be.. it's not.
EDIT AGAIN: As far as building your legs up.. yeah I guess run and ruck but actually go do squats and leg presses and ****.. works wonders for your muscle mass /strength all around.. wouldn't know what selection would be like had I not been working legs in the gym.. probably woulda been harder but iunno