Having reached my target of Baron (so I could buy the Clipper) on Saturday, this is how it went...
The most consistently high scoring missions were the 'deliver classified data' ones, which involved taking data from A to B within a relatively short period of time (long enough, but measured in minutes). You would have to avoid scans, getting scanned failed the mission, but as most were to deliver to outposts arrivals weren't usually scanned anyway. (Stations and Military outposts DID scan, so high speed stealth delivery for them).
I tried the odd classified data delivery that involved delivering to an NPC in a target system - these seem pretty broken to me, I'd hang around the target system - often unable to find the guy - and I'd get a mission update to go back to where I collected the data, then I'd be unable to hand it back in. I completed one of these at some point, but it didn't score well and took far longer and was confusing as hell
Missions to kill NPCs usually involved the target flying an Anaconda in a 2 or 3 man wing.
Anything involving a rendezvous make sure you have a frame shift wake scanner!
From Master through Baron the best missions were classified data delivery, second best were the rapid delivery ones (mission symbol a cargo canister with an arrow) - straightforward courier and 'go fetch commodity X and deliver it' missions often produced only a fractional increase in rank - by knight it took 2-3 of these to climb 1%, doing the Lord ranking I found it took anything up to 4 or 5 missions to gain 1% doing simple deliveries.
The charity missions (donate x credits) were always a good earner for rank, even small donations returned a couple of percent. sometimes 5 or 6.
There seemed to be a tendency to get low scoring missions on the bulletin boards until at 50-60% in the rank, then suddenly there'd be more of the higher scoring ones appearing - don't know if this was really the case on purpose, but my record consistently showed that from 20-50% in each rank took a lot more of a grind than the last 20-30% or so.
Dave