Hey. Each person has their own unique way of doing things. Is there really a "correct" method to kill something? In my opinion, it's best to RS gold blast them with your strongest weapon and equipment, all the while raising the intensity! But I've not killed one. You can simply cancel the task that is most difficult and/or the one that you are most annoyed with. Why continue with an activity that is slow?
I'd cancel Black demons. Heard those are bad. Kalphites are quick and can provide you with quick Slayer points. It's not necessarily a slayer's experience, but nevertheless, it's a quick task.
LRC is very profitable It's what I've heard. The average is four to five thousand dollars per job and that's quite good over the long term. You also have a shot at the Patriarchs. They instantly drop around 200k. Pretty dang good. They also offer good experience, I believe.
Don't fret about the mineral content. They add time, and according to me, is not worth the lost experience. Ugh. Hellhounds. I'd block those. They're only good when it comes to clue scrolls and charms. Charms in gold, that's... They are cannonable, though.. I would advise against blocking bloodvelds. They're great and fast. The drops aren't as bad, though. If you're looking for cheap OSRS gold a reference to any monster, check out this wonderful one made by Azarath.