Play your rounds in the propulsion skill (or preception, I'm not sure). When you reach prestige 1, it will release the formation button, which will release an empty formation stone. When you insert 3 red rounds, it activates. It accumulates XP when placed in up to 3 skills. When it reaches its maximum, it can give a 4x skill speed boost.
Regardless of the skill, it collects XP at the same speed, so use the time it takes to maximize your rounds. After maximizing them, go after the strange stone to increase the round limit (you may need to sacrifice rounds again to reach it). Then, maximize your rounds again and sacrifice them to reach the star. Then, release the reducers, which are actions that reduce the time it takes to perform travel actions, such as polpusion, by 10% (for each time I did this, I managed to reduce it from 1,000 to a little over 300, using my rounds in the first 4 or 5 trips). And that's when I stopped and closed it, and came back today to find out that it didn't save my game.
NOTE: ALL THE TRANSLATION OF MY COMMENT WAS DONE BY GOOGLE TRANSLATOR, MY ENGLISH IS VERY POOR.