I just bought Dark Souls finally as well. Go to the dark souls wiki, it will help you out a lot. Even though I played Demons Souls, Dark Souls is more difficult to figure out how things work, so I find the wiki helpful. The game is very trial and error even with a guide.
From what I read the warrior is a good melee beginner character, the knight as well being a tank character. Pyromancer is easy for starters as well if you plan on using magic. The bandit starts out very offensive, the theif has high dexterity and is more rounded for melee and magic but harder to use than a pyromancer and doesn't start out with magic capabilities. The sorceror is a great magic starting character but very weak at the start. Deprived is pretty much terrible.
I chose a theif just like in Demons Souls, but I am experienced. Dark Souls seems to have a higher starting difficulty because of its openness, though not being in human form doesn't half your health so I guess that is easier. Oh, the gifts are pretty meh. The master key can be found or bought and so can everything else. The witch's ring requires an item to trade to aquire, so that is the hardest to obtain I guess. That ring and the pendant are story items. The black firebombs can help you kill the first demon, though you can just avoid him.
I'm loving it so far, good luck.
Before the PS3 everyone was nice to me :(
