Well for starters, what have you chosen when leveling up?
At low levels, your holy trinity will be flank attack, twin fangs, and stealth. Upgrade flank attack ASAP. Next order of business is evade.
Level 1) start with twin fangs & stealth (default)
Level 2) take flank attack (DW tree left side)
Level 3) upgrade flank attack (DW tree left side)
Level 4) get evasion (it's crap but you need it for evade) (Subterfuge left side)
Level 5) get evade (Subterfuge left side)
Level 6) passives dance of death (DW tree right side)
Level 7) passive sneak attack (DW tree right side)
If you look for Matt's pre-skyhold build it'll help you get further along.
So how do you use this? Basic attack sequence is: run up to something (it'll see you and turn to you), flank attack (you're now behind it and in stealth), wait for the enemy to turn away (probably to attack Cassandra, Solas, or Varric), then twin fangs. If the enemy is running too far away from you, you'll need to follow it and then twin fangs.
The DW Creed:
Always attack from the rear
Attack from stealth if at all possible
Pay attention and avoid AoE damage from 2Hers, bears, etc
Upgrade flank attack really helps out, and gives you an easy way to get into stealth with a short cooldown. Use it...a lot. It may be odd I'm emphasizing stealth, but you get a 50% chance to crit from stealth. This is extremely valuable at low levels when your gear doesn't have much crit on it. And things really pick up once you get the sneak attack passive (it doubles your crit).
Just keep at it. DW is very hard the first 10 levels. But eventually you get to the point where you will just laugh at how you slaughter your enemies with ease.
Also, take advantage of cross-class combos. Make sure Solas is using winter's grasp and drill down further into the tree for ice mine. If you use twin fangs on someone frozen, you will do a LOT more damage from the shatter.
Also, as soon as you can go to Val Royeaux and buy the dagger schematic from the shop there. Sacrificial dagger schematic if I recall correctly. Easy tier 2 dagger schematic.