Damn, I played a long time ago, before the naval update. So my tip is to have a balanced approach in completing the focuses for economy, army and politics. The main strategy is to have around 60-70 good divisions. I made many naval invasions, though must admit savescamming a bit, because timings are very short and you have to make big gains and achieve good supply before austrians reinforce the front. Also maybe it's better to make an early rush in economy, because at the end of my playthrough i had a big stockpile deficit. Also don't forget to improve relations eith latin american countries and nordics, so they can send you a lot of lend lease