I used a Freight-courier with Neutron turrets. Cannons could work, I guess, but turrets do the job a heck of a lot easier, in my opinion.
Take out the fighters and other ships(Frigate, Cruiser) first. They are a pain in the neck if not taken care of quickly.
Make sure that you are drifting (away from Dreadnought) and in the right position(within your weapons range and out of the Dreadnought's) before you start firing on the Dreadnought. Adjustment of position may be necessary as the Dreadnought can catch up to you.
Be patient. Even with Caps Lock it takes a little bit. Time may vary depending on what weapon you're using.
Finally, someone tell me if I did something wrong in making this big post...