I figured out the bicycle kick and headbutt on my own. Without even using them effectively like you mentioned, I was winning like 7-1. I'm sure that'll change when I actually do those specials after the ball is passed to me.

I wish there were a stamina meter or something in the game so I can tell when one of my players is wearing out and know when to keep him away from the ball (and hence not getting slide tackled).

Through GameFAQs I learned that to do those super shots where the ball changes appearance and knocks people out is based on the amount of steps you take before making the shot. On the USA Team it varies per member (either 7 or 3 steps), but for the rest of the teams, each member requires the same amount of steps (differs per team, but usually 3, 5, or 7). So you catch the ball, take the required steps, stop, then shoot. Pretty simple. You get 5 of those shots per half if I read correctly. I don't know if that includes the pass -> bicycle kick/headbutt.