To get the best game scores, turn off all victory conditions and win a military victory. Whether you blast all the aliens to bits or culture flip all the major aliens' planets still counts as a military victory - just make sure to turn off that culture and tech victory and don't make alliances.
To get higher scores, research all the tech. In my experience this adds 20% or so to your score. In addition to this there seems to bonuses for population, society, and economy. I have found that getting all the resources at the end adds some points although I am not sure how much and it may be because the resources boost the above-mentioned, military, economy, tech, morale (population), and so forth.
As far as the metaverse, my experience is that there are two broad approaches. One is "quality" and one is "quanitity" and players can mix strategies. I guess i am a "mixer" LOL.
The "quality approach" to reach the highest per game score is to play as difficult as you can play well on the largest map. Some wins on the gigantic painful or masochistic maps are yielding 25k game scores! Anyone who can get a 25k score really knows how to play. Anyone who can win on masochistic, especially the bigger maps, knows how to play. I have never come close to that (my high game is about 16k) - so much for the "quality" of my game. LOL.
In the "quanitity approach", the metaverse rewards frequent game submissions. So cranking out 6 to 10k games on Tiny/Small will get the metaverse score up there even on beginner games. Look at the ultimate king of crankers, EBZeroMatrix, who is top three but doesn't play painful, masochistic, or even challenging games. And you won't see EBZeroMatrix play large maps because they take more time. EBZ can play a tiny/beginner game in 20 minutes that still takes me 2 hours so I am not sure I will ever be a crankster either. I have heard of no other player who can complete a game in 20 minutes. It boggles my mind.
In summary, the player strategies that work best depend on the skill level of the AI and map size. The best quality game strategy guide is the Orion guide at http://www.orionsector.com/pages/galciv/downloads/The_Unofficial_GalCiv_Strategy_Guide_v1_0 and EBZ's Gal Civ Cranking Guide is at http://ebzeromatrix.tripod.com/
IIRC the metaverse score uses the summary of scores as the numerator divided by the square root of the number of games submitted. Algebraically, you can see there is a reward for not only the whopper 20 to 25k games but also a reward for submitting dozens of games over a short period (cranking). Also IIRC, each submission period is divided into a one month block and scores beyond 1 month incurr some degredation. However the degredation is not dramatic and those who have been playing since April are harder to catch than newbies like me.
I think it is fun to play both the quality games and then if you get overwhelmed by moving hundreds of constructors and think, "Is this game ever going to end?", then play the speed game that EBZ perfected. Go back and forth. One of the best things about Gal Civ is the 10 levels of difficulty, the adjustments of habitable planets and star density, and the good v. evil moral choices that open up different parts of the tech tree. There are sooooo many combinations and different strategies for each. Just keep it fun. Hope this helps.
Rick