Sorry but they were IMO never going to open up the first issue to new authors, its the hook to get folks who did not pledge at a level beyond getting the 1st issue to sign up for more. The 1st issue that everyone gets, per Sartis, is supposed to have their submission guidelines.
Do's
-3-7k words
-character-driven (rather than technology-driven)
-any era
-'mechs not required (but they are awesome)
Don'ts
-something not set in the BTU
-romance. supernatural, fantasy, or horror as the main focus
-excessive sex, gore, or profanity (keep it PG-13)
-lengths outside of the word count requirement (longer works require you earn your stripes)
-Vanity stories, personal units, author-as-character inserts, narrations of tabletop sessions
-publically available fiction (if you posted it, you can't submit it)
published works get five cents per word ($150-350)