[When I started, my wife used to say I was out there selling 5 days a week just so I'd have a paying client for the weekend.]
Building a reputation is a full-time thing. Once you've figured out what makes you a better choice than the competition - whether it's your talent, friendliness, industry contacts, or whatever - everything you do has to support that USP. Surely you picked up some kind of reputation at the post house... build on it. If you're not sure, invite some of your old clients to lunch and ask them. They're media people and would probably be glad to give you marketing opinions. Even if you have a non-compete with the post house, it surely doesn't say you can't take someone out for a drink. (IANAL)
If you can't compete on one of those bases, you'll either have to compete on price (which can work when you're starting out, but becomes is a race to the bottom that can kill your business) or gear (which means you'll be clobbered by the next well-financed studio to come around). "Just give me a chance," isn't a good pitch by itself, unless you also give the buyer a reason to try you. Otherwise, it's a lot easier for them to call the folks they worked with last time.
So having a niche is an important part of your networking. Don't just say 'hi' at a get-together; mention what you did lately that points to your niche. Put your story in local media (as PR rather than ads, so the reader can accept it better). Keep coming around with your new and amazing reel updates.
And if the place is slow, either
a) Take on some pro bono or dirt-cheap promising student/indie project, where you can show off your niche; or
b) Take a break. Make sure your gear and books are up to date, then have some time off. You'll pay yourself back when there's a project in-house.
Worked for me...