I'd tend to go for lv 4 stealth, trapmaking, coercion (we're all bad at that word, right?...), 3 in the top Rogue line and 3 in the second line if im a cunning rogue.
Dex rogues are so powerful you can go naked in the later levels and get dealt hardly any damage >=) (maybe it's because the rogue was naked? - there is a vid of a dex rogue beating up that half-scripted (the scripted part is the bit when they appear) fight in the Orzammar palace.
oh, weapons? Roses Thorn + Dead Thaig Shanker (or another dagger that i've forgotten about)
It'd be best to get some CC traps, place them inbetween your group (who should be on hold) and a group of foes, then get just out of range of the CC traps and get a member of your group to come forward, when the trap is activated (doesn't have to be a trap, early on in the game you could use morrigan with the paralysis explosion glyph combo - though the paralysis glyph is seen as a deactivatable trap in a rogue's eye O.o) and rush in behind them and they'll be dropping fasting than a stone dropped into water....
Tactics I hate, mainly because they're either, A) so gimmicky or

they don't do what they're supposed to >=/ which is why I hardly ever get the tactics skill line (unless it's a mage, then i'll get a few more because they have too many damn spells), and the combat skill line should be a must w/e the build...
DW should always get momentum and DW mastery (just for that added versatility and the fact that it offers some bonuses in that line), those, I find, are the two most important lines in a DW character (momentum is like a spaz mode and DW mastery line buffs your attacks a bit, i find the middle line a bit... useless because when you use a skill, you tend to be lowering your dps...
and Haste + momentum actually makes you so much of a spaz that you slow down! so only go one or the other!
Stats?
Str 20-24 (depending on if it's awakening or not)
Dex 36-Max (36 if your a cun rogue, otherwise max)
Cun 16-Max (16 is minimum to get the coercion line)
Will 20, the only time it gets up to 30 is when your a heavy spell user.
Con useless unless your a tank
Mag same with con but unless your a mage.