1) Not really, nothing unique. Stay in character, emote at appropriate times to add to the atmosphere, things like that.
2) Adding on from the first question since they're similar in regards to creating RP, Wardog4445 impressed me recently with the depth of his craftsman RP. Instead of simply making a bed and giving the item to me I arrived at his shop the next day to find a placed bed with a sign near it saying that it was newly made. This led on to some pretty in depth home renovation RP - I had to remove some railings on my loft in order to RP'lly lift the bed up there. It may sound boring but it was quite entertaining. So, just little things to immerse others in the world can make all the difference.
As for finding roleplay I've never really been too lucky on the count until recently. I spent almost the entirety of my time in Asulon wandering from place to place looking for RP without success - that turned around when I actually settled in one place and found a group to RP with - in this case House Guivret in Ursakar at the beginning of Orenian noble house RP, which led to some pretty interesting adventures and just normal times at the tavern, gambling and drinking. So, my tip would be to settle down. Find a town with decent activity and add to that activity with your own RP. If you're a human player or human inclined I still recommend Orenian noble house RP - I'm biased, but off the top of my head the Stafyrs are a good example of nice RP for commoners and noble family members. Other races? Depends on your play style. I've never tried High Elf RP but I've heard only good things about it and they're by far the most active community by town activity over the years. Leyulin's had the best Wood Elf/Standard Fantasy Elf/Aegis-Malinoresque RP in ages recently with good activity - not too sure how the community will fair from the move further south but time will tell. Can't speak for the Orcs or Dwarves. Guilds and organisations are always nice sources of RP but I wouldn't rely on them too much - still, if you can find a consistently active and interesting guild go for it.
3) Three main reasons:
Lack of motivation to leave, probably. Things can be **** here and people ***** and moan endlessly about the smallest things but I can't be arsed finding a new RP community, let alone one that would be around long enough doing the sort of RP I like.
Friendships made and familiarity with the community on here. You can be bastards but most of you are okay really.
I'm no longer in main school and I'm currently unemployed until I go to uni in september, so boredom.