People try to get too fancy. The basic idea is:
/script AcceptBattlefieldPort(1,1)


That is all you need to accept "Join Battleground?" when it pops up. People use /run to make it shorter than /script. People try to add more accepts (if you queued for multiple BG's). I just join one BG at a time, so I just use the one accept part. A new item I LOVE is:

/click StaticPopup1Button1

It works for WG starting. It works for almost everything that pops up a click button box. I stole it from a rogue poison macro that someone made. I put it in my accept all macro and love it.