Write, write and write.
Almost every position at BattleTech is filled by those that were doing it anyway, and got noticed. From writers to demo agents to sculptors to artists to web developers. (And even for Moderators, while giving posts and bans to other forum members pre-Moderator status is discouraged, having a record of polite forum posting is a good history to have..).
Battlecorps was the best entry in to fiction writing. It's on hold at this point though.
I'd say look at what series BTech is doing, and write something for that series. (Touring the Stars, Turning Points are the two that spring to mind). Then see if Brent, Ray or John is interested.
Or just write your stories however you want and post them as fan fiction.
I'd note that novels are not at all likely to be considered from somebody new. Even relatively experienced BattleTech writers aren't getting looked at at this time. It pretty much has to be somebody already with something published. (Because it's not just talent, but selling bookstores/distributors to carry them, and BT needs the push from experienced novelists more at this point than BT is a help for getting novelists exposure.) That's AFAIK at least.