When you guys watch covers on youtube or listen to music or anything, how do you figure out the strumming patterns for songs? any tips, or techniques? thanks!
Generally I just listen to the song a lot until I have it memorized, then do the trial and error bit until I get it right. It also helps to play along to the song as often as possible, you'll start to pick it up as you go. That or listen to the song, then strum a part until it sounds the same or similier. That's about it.

Hope that helps
I agree with Garou1911. Its just a matter of listening and trial and error.
your best bet is to make sure you know what chords are being played first. then make sure you know if they change them, because any little change can make quite a difference. Then you sit there and just play around with them till you can get that similar sound. You can also distinguish between a upstroke and a down stroke depending on the chord, so try and learn to use that.