I saved almost all of my skill point on dagger until I had it mastered, then I maxed out eviscerate and vipers nest. Eviscerate does up to 493 damage when maxed, and vipers nest does up to 580. I put three skill pts on swipe to use while leveling, as well as one on each of the throwing skills.
Even after I mastered the dagger, I saved 5 skill points until after I mastered cutlass earlier today, and then put those on the passive "Blade Instinct" skill which increases all cutlass and dagger combat damage by 25 percent.
The only thing I think I might should have done differently was max out sidewinder instead of vipers nest. Vipers nest will damage all the enemies within its range of effect (or just one if thats all there is), but the damage is divided, I think (I could be wrong about that). It also takes longer to recharge.
One skill point on sand is good for leveling, as is putting just one on some of the other skills. They don't do much damage, but you get skill pts for using them.
Good luck, where ever you decide to put them.
