For an Interwebs friend who wants that 3-star achievement but also doesn’t want to watch a ‘this is how to get teh best tiem evar’ video. (Bear in mind that I’m still working on getting 3 stars on all my dashes, too, and that we can’t all be Woody...)
1) The first time you do a Dash, don’t worry about your time--instead, focus on understanding where the end of the Dash is in relation to landmarks. The arrows given to you by the Dash are usually one of the slowest ways you could ever get where you’re going. User Races have checkpoints that make you take a specific path, but the Dashes that count for the achievement only care that you pass through a specific starting line (usually extends to about 20ft left and right of the marked red line) and that you end up at the finish dot.
2) Look for ziplines, even if they’re a little out of your way. Ziplines and MAG swings are quite fast ways to get around. CAUTION: avoid crash pads, as they’ll slow you down almost as much as a hard landing.
3) Look for ways to wallrun-jump to cross gaps or get to higher ground; a forward climb can really slow you down, but a well-timed wallrun-jump has the potential to completely clear a tall ledge.
4) Look for ways to descend gradually, even if they mean veering slightly off a straight line. A straight drop to a run will ALWAYS be faster than a long drop into a Skill Roll.
5) Coil over anything that you don’t need to vault off for altitude. Sliding will slow you down, but coiling will sail you over anything waist-height or lower without even touching it, and will let you slide over most shoulder-height obstacles.
6) If you DO slide under (e.g. through a low opening in a wall), consider hitting shift to roll and come up running. CAUTION: this can lead to you planting your face against the next obstacle or rolling casually over a ledge.
7) If you feel like there must be a gimmick to the Dash, you’re right. There is always at least one clever shortcut that will take 10+ seconds off your time, and this is the route intended for a 3-star rating.
8) Practice your jump timing. You can shave off half a second by perfectly timing an upward motion over an obstacle, which allows Faith to keep ‘flowing’ without losing momentum. You can even use a well-timed upward motion to break a long fall by landing on a railing in some areas, turning your long fall into a simple vault.
There is more than one way to cause an "unintentional suicide." As far as can be ascertained, shoving, sliding, or otherwise knocking a person over a rail or off a roof does not count. Walking a possessed person through a rewired Wall of Light does not count, neither does being shot while possessing an enemy.
The Bend Time way: Piss off a baddie and wait for him to raise a ranged weapon. Use Bend Time 2 to stop time as soon as the bullet leaves his gun, then use Possession 2 to walk him around in front of the bullet. Leave the guard (being careful not to get between him and the bullet) and then leave Bend Time.
The Wall of Light way: Rewire a Wall of Light to harm enemies. Use Possession 2 to take over the enemy, then walk him near the Wall of Light--not into it, just close. When you leave Possession, he will stumble forward a step or two to be violently ill, and if you have judged the distance correctly, he'll stumble into the Wall of Light. The masked party guests at the Boyle party are a separate faction--you can walk them into the nearby Wall of Light without rewiring, though it is recommended you get rid of guards first, as they will attack as soon as you leave Possession.
The Wall of Light way (no powers): Rewire a Wall of Light to harm enemies. Hide on the opposite side of the Wall of Light from several enemies, then make a noise to draw them toward you. [It is not confirmed whether this never counts or simply doesn't count on certain missions.]
As far as the "Lights Out" secret achievement for Dishonored is concerned, rewiring is equivalent to de-powering. (The achievement wording only says "You deactivated at least 5 security systems on Kingsparrow Island.")
The five most obvious systems are the watch tower slightly to the left as you face the lighthouse from Sam's boat (which can be difficult to get to without Blink 2 and Agility), a pair of Walls of Light (accessible through a small tunnel in the wall to the right of the harbor platforms), an Arc Pylon on the beach toward the right as you face the lighthouse from Sam's boat, and another Arc Pylon on the aerial platform between the gatehouse and the lighthouse itself (getting to the whale oil on this one can be tricky, and it's much easier to Blink your way to the control box and rewire).