In response to a question in the comments here, this is a quick synopsis of how I ended up in Business Development, and things I think helped, and things I think were not so useful...
Did Ph.D. in immunology. Was in Boston when I did this. The course of my Ph.D. got me doing computer programming (building microarray database and analysis tools for my own use) and a bunch of in vivo work (mice) and molecular biology. A total hodgepodge, but interesting stuff nonetheless.
In the course of that work, I became disillusioned with the life of an academic researcher and decided that this was not the way forward for me. I wanted more adrenalin, more frequently, and with more stress. The thrill of discovery, when something worked, was/is AWESOME, but it was infrequent and I am impatient and have the attention span of a newt.
So I decided to go work at a dot com company... unfortunatly, I didn't finish fast enough, so in the course of writing the dot com crash happened (2000 ish) and so those jobs went bye bye. Then I graduated and was unemployed for awhile and essentially applied to every job that I saw on-line, in the paper, or heard about. I called every recruiter I could. I wrote letters to everyone whose name I could lay my hand on. I worked at JP licks to earn money (ice cream place...) and played WAY too many computer games. My wife was not happy with me. This period sucked.
Then a recruiter called me to go to an interview at a start up bioinformatics company to be a application scientist. I had no idea what the person was talking about, but operate on the assumption that there are very few people that I don't want to talk to and that interviews with real companies don't grow on tree's. So I went and got hired. I did that job for 3 years to the day, and from there moved on to my current position in business development.
That is how I did it.... What did I think was important.
I don't think you can go direct in to bus dev from your Ph.D. You don't know anything about the business side of things. You have to go to the field in some capacity to learn something. Internal positions, be they at the bench or in technical services, MAY work but I haven't seen them work. Noone that I work with or interact with came in to business development that way.
The problem with internal people is that they, out of neccesity to be good at their job, have a primarily internal focus. Bus dev is, by definition, very worried about how the company fits in to and succeeds in the external world. The two are, obviously I hope, very related in that you won't succeed if your company is screwed up internally and that no matter how good you are internally if you don't watch the rest of the world (customers) then you won't succeed either.
Getting that first job is, to my mind, the absolutly hardest job to get. You are unproven and we have to take a risk on you. You have no relevant experience (likely) and we have no idea if you are going to break from the travel. If you haven't done serious travel, then you have no idea if you are going to break as it is on the list of things that you can't know before you do it. Some people love it, some people hate it, and some people just do it becuase that is what you have to do (that would be me...) neither hating it nor loving it.
We also have no idea how you are going to do with customers. There is a lot to learn there, none of which is really teachable until you are out there getting beaten up.
SO - To get the job you have to be persistant in a serious way, and you have to be prepared for it to take multiple months (5-6). Taking a post-doc is something a lot of people do (I didn't) that gets them more scientific experience. I don't think it helps you on the business side, and in fact I think it just sets you back a few years.
You have to really really really know that you are good at dealing with people. If you are an introvert, this is likely a bad decision. Stay in the lab.... If you HATE public speaking, probably not a good step either, although you can work around and practice your way through that one.
Apply for every job with every company that makes any sort of lab equipment you ever used, sells any sort of reagent you have ever used, or is a competitor of those folks. Look at their web sites for "Field application scientist" or "Application specialist" or "Associate product manager" or " Field scientist" or things like this. The associate product manager position gets you in to the marketing track and is another great way to move toward bus dev.