Hey guys, I found a decent way of gaining ranks! Ignore everything but the cash rewards. The more cash you get from a mission the more experience you seem to gain as well. Find a system that gives a lot of smuggling missions, as they seem to pay the most.
I am in an Asp, with ranks Competent, Broker, and some low explorer rank I can't remember just now. Anyways... In a system with 3 Empire factions (or whatever they're called) that I am allied to, I get smuggling missions that pay up to around 600k. Sometimes I'll grab two that pay 200k and go to the same system. I don't bother with less than 200k, preferably I want more than 300k as a combined reward for a single trip. I also grab any low paying transport missions to the same stations. I am now Lord, and I expect to reach Baron tomorrow in a few hours.
The grind isn't that bad, since I'm making so much money. In fact I don't even want to upgrade my ship that badly anymore, since I'm making a ton of money just doing these missions.
Smuggling is no problem. I usually just boost towards the station opening, and activate silent running. If anybody scans you, just pop a chaff - not right away, but let them scan you for a moment first, that way you'll have a better and longer effect of the chaff (Edit: or rather the longer you can postpone the scan completing). Found this one out myself too.
EDIT: I did it! Two and a half hours from Lord to Baron. I didn't fly very effectively either. Here's what I did:
About 30 charity missions that happened to pop up.
Smuggling runs worth around 7 million credits.
Pretty quick if you ask me, especially considering the money I racked up in this short time.