Yeah, I haven't done a personal blog in awhile, so I figured why not post one now. *shrug*
!. Do not mention that the main character is a Brony. First, the reader already knows you like the show, because you're writing a 1000+ word story in the first place, so that point is redundant. Second, for shipping purposes if you chose to go that route, it makes the protagonists out to be some kind of creepy inter-dimensional stalker.
2. Keep any weird/disturbing fetishes to yourself. Yes, I'm talking about the diaper fans out there, just because you like the idea of fermenting in your feces doesn't mean others need to know about it.
3. Go easy on the cliches. "My HIE is an ex-military bad ass that was in (insert conflict here), he was lonely and killed himself and now is the key to saving Equestria from a vague and evil threat." Don't get me wrong, I completely understand the idea of giving a character a military background as there has to be a way to show that said hero can kill like a Category 5 Hurricane made out of bullets. Maybe you could be more subtle about it. The same goes for the rest of the cliches, mix it up a little bit.
4. Make the HIE likeable or at the very least have said character grow and mature. In addition to that stop with the random cursing, this isn't an early 90's OVA English dub. I'm not a captain morally, but I've read enough fics where Character-A will say "f**k" just out of nowhere, now if the character stubbed his/her toe or was dealing with a villain and called them a mother f**cker before ripping their spine out through their ass, then it would be justified.
5. Don't have characters loose brain cells for plot convenience.