Milestone Leveling
Player's Handbook · Appendix B: Recommended Variant Rules
I won't delve too far into this. The simplified version is that instead of receiving experience for every encounter and leveling up at odd times, the GM chooses when they level up. Additionally, there never has the potential to be an experience, and consequently level, disparity between players.
Why I Recommend This Rule
Milestone leveling eliminates unnecessary record-keeping, helps maintain narrative significance to leveling up, and streamlines the GM controlling the game.
Additionally, if you utilize the Space Combat optional rule set, I urge you to use this. The nature of space combat is that there is no ship leveling up. Experience values relative to the amount required to level up will diminish drastically.