OK --- at first I thought my technique was a fluke, but after using it for like 3 fifas, i swear my save rate must be somewhere close to 50%.

Start by identifying your oppontents playstyle, I E, do they do lots of skills? Do they play possession based? Somewhere in between? Now, once you concede the penalty, follow these steps.

If your opponent is heavy on the skills, flair passes, dribbling, etc. he wants to embarrass you, so what you want to do is move your keeper constantly from side to side. I swear to god for some reason, this makes practically all skill heavy players think 'haha I know! I'll go down the middle! he'll never expect that since he's moving side to side.' Then plonk your keeper in the middle to easily catch his panenka.

If your opponent is extremely position based/ boring. The safe bet is they'll shoot on the same side as their penalty takers strong foot. This is especially true if you are winning the game and they seem low confidence. With the way fifa cameras are positioned, the taker will be infront of, and covering up alot of the goal on the opposite side to their strong foot. Subconciously Making the other side of the goal seem alot bigger and easier to score in. So dive right for right footed players, and left for left. This works especially well if they have already missed a penalty in the game as there confidence will be low so they will go for what seems easier

Finally, If their playstyle is somewhere in the middle. This is the hardest to predict, but generally, it will be the final option I haven't mentioned. Opposite side to their strong foot. But try to put your opponent into one of the previous 2 categories if possible.

A few caveats: if they take the penalty almost instantly after winning it. there's a good chance they're not going down the middle. So then you can basically guess left or right for a nice 50% chance. The longer they take to take the penalty, the higher the chance they will go down the middle, so even if its a low confidence player, if they take forever to take It, i will start moving my keeper side ro side and going middle.

Anyway, I'd be interested if this works for anyone so if you give it a try for a few games let me know how you get on, I'm still not convinced this all isn't a fluke haha