What tweaks should I make in order to make this deck better?

https://deckbox.org/sets/812359

Craig Wescoe just posted a Jeskai tokens list over on tcgplayer that'd be worth looking at to see what changes you might want to make. I also recall Frank Lepore having a video deck tech with a Boros token build (http://magic.tcgplayer.com/db/article.asp?ID=12101). Neither is straight Mardu, but it wouldn't be hard to make the appropriate changes (toss in a few Thoughtseize, Mardu Charm, Butcher of the Horde as a finisher... pretty much call it a day). Obviously you should deviate to match your playstyle, meta, and whatnot but it'd be a great place to start. After you've given those look if you still have questions I can give your list a closer look.