This is a very nice guide for beginning players. I would add one comment to it;
Deadmines can be done by 5 level 16s who are prepared to work well as a group and learn from mistakes.
If you take a disparity of levels then you have to be aware of the possible outcomes, the most likely is that if you have a L20 mage and a L16 tank then the mage WILL get aggro.
Some classes can shed aggro, rogues can vanish, hunters can feign death but probably not at deadmines level. Mages however have no way do shed aggro and they deal damage in big lumps, the rogue will inflict the death of 1000 cuts and can stop if their threat builds too high, if the mage crits with a fireball it's Boom, Aggro.