The best way to practice prediction skills is still by playing openers. The immediate gratification factor plays strongly to our psychological reward mechanism. You saw that personally in your American Sniper performance, and also with Spongebob.
A portfolio your size can be strongly influenced by your opening weekend plays. However, continue to keep a percentage of your H$ in starbonds - the slow but consistent gains can help offset incorrect opening wekend calls.
The MOST IMPORTANT thing is not to give up, continue to experiment, understand that this game comes with HIGH HIGH'S and low low's, so balancing your outlook/emotional state is crucial.
Also, keep Vegas in mind. Unlike blackjack, you CAN chase your losses (or winnings) here at HSX. If something bad happens this week (of this MONTH, in my case) it really won't matter over time because something good will happen next week. READ EVERYTHING IN THE FORUMS (especially the MOVIES and STRATEGY forums). Stay consistent. No one ever got good at this game by not playing :)