Many actors...especially those new in the business forget that it is a business. Plain and simple. In order to move forward with your career, you must at least attempt to master the business side. What is the business side of it you ask? Firstly, its your brand? Who are you? What is your type? Are you the naughty mean girl who gives no one a break or are you the nerd whose only friend is her pet rock? You basically have to typecast yourself. If you don't know who are, Casting Directors won't know how to cast you.
Do you have headshots that aren't crap? Bad headshots are worse than no headshots. Find a good headshot photographer and really take shots that capture you're "essence" as an actor. Christopher Dietrich, an Executive at Actors Connection calls headshots "Essence Shots". Keep that in mind the next time you get headshots.
Resume. If you don't have one, make one. Even if you have to work for free, if you don't have a resume, no one will take you seriously. Submit to projects you're right for even if its unpaid. Your going to have to work for free sometimes...unless your fathers name is Steven Spielberg.
Do You know what shows you're right for? Do you know the Casting Director for those shows? You have to do your homework. It sucks, but it must be done. Research the shows you're right for then, send mailings (headshot/resume/cover letter) to the Casting company who works on that show or production. So you want to be on Modern Family? Look up the show on IMDb and you'll find that Jeff Greenburg cast 67 episodes. If you dig a little deeper you'll find that Jeff has also cast other awesome shows like "Frasier, Up All Night and a bunch of TV movies. Now you have to find Jeff so we can't send him our stuff. Its YOUR homework so do it!