Prep is always the biggest part, if you are increasing the level of gloss you'll want to be very careful to make the walls smooth.
Whoever did the original prep on my house did a real slap-dash job of it, so I go over nearly every seam on both sides. I also take the opportunity to fix nail pops, I remove the nail without damaging the surrounding drywall and replace it with a screw. I can paint a room in about a day, but the drywall prep usually takes some time.
Some of it has been really goofy....like having skipped taping the seam all together, or having skipped coating the tape...lol. The previous owner did not seem to care at all and neither did his painter, because they simply painted over all of that stuff. Cracked seams on the ceiling that someone used paint to fix....and not surprisingly it did not fix it for long.
So, I feel your pain.....and oddly enough, at this point I sort of enjoy it. Seeing a wall, painted in eggshell, that does not show seams or nails is a uniquely satisfying experience.
Side note, replacing the ugly as sin contractor grade fan in the bedroom....honestly would like to just ditch it all together, but my wife is convinced we need to have a fan.
Edited by SkinnyGoomba - 12/20/15 at 12:20pm