Cloning is simpler than most ppl make it out to be.. A Tiny bit of heat from the underside is good (don't cook them!).. Its actually the medium temperature that you want around 80° or so, the air temp can be a bit lower which helps keep the RH up.. I usually don't seal the dome right up, I spray them a few times a day, if its humid enough you should only need to dunk them in water a few times I find, but don't let them get too light until you're positive they are growing roots..
An exacto-knife is ideal to make the 45° cut.. Slice it don't chop it! Rooting gel is good, but not critical.. It probably helps most by sealing the stem immediately away from air, but I would say that you get better growth for the $5 investment..
Open up the hole in your cube/pellet a bit with a toothpick to get the clone in cleaner, then gently squeeze it to ensure good contact..
Temperature stability is good, so I keep them on 24/7 until ready to plant..
If you have big floppy leaves on it, its probably best to trim them down in size but leave the ends of the lobes and a bit of green..
A good sign is yellowing obviously caused by cannibalism.. When that happens you can be pretty sure that roots are growing.. Browning without yellowing is not so good..
Some plants are easier to clone than others, but most aren't tough at all.. A safe bet would be to expect 70% success rate I think, but don't be surprised if you get closer to 100%..