The actual formula for how the weight of ratings work was released once, then hidden again, then reworked, then the post was probably lost to the ages. It is dark knowledge held only by the elder scribes and people who have the power to look at site scripts and shit.
However, if you'd like my rough estimation, if guests have any effect on ratings, it's very little. You only tend to see impact with people in the 500-1000 points range and higher.
A fast way to do it is with reviews. Rating gives you one point, then getting a featured comment will give you 2 commendations, whuch tend to be worth points, then you get 10 points a day whenever you get the most commendations. It's feasible to do in under a month even if you don't rate near 500 stories.
Or you could just write a bunch of games, if they're good enough to be commended those can be like 60 a piece for anything of a few thousand words.