Quick question, how should I skill spectre? Q-E-Q-W-Q-R-Q? Then max W, then E?
Like most heroes, you want to skill her based on the match. Unlike games like League of Legends, there is usually no concrete right or wrong way to skill a hero.
If you're under a lot of duress in lane, it may be best to skill more early points in Dispersion to both reduce the damage you're taking as well as punish autoattack-happy enemy laners.
If you expect to be actively fighting or otherwise trying to secure kills in the early game, you'll want to have more points in Dagger. If you're in a tri-lane, this is most likely what you'll be looking to max out first. Spectral Dagger is always taken first point, as it's your escape mechanism at minimum. But maxed first, you expect it to help you set up kills with some cc support help. Some max it first, some max it last. You can decide based on the match whether having the 200dmg nuke + 40% net movespeed advantage (-20% for targeted enemy, +20% for you) vs a single target is the best plan for early game or not. If you're planning to fight and chase a lot early, go with this maxed first.
Desolate is her best ability but you only get the buff when a target is alone, making it strongest when used in conjunction with the ultimate on isolated/retreating targets. This generally makes it the weakest laning phase skill, but a skill you usually want maxed first or second so that it's ready to do work once your big items start coming (rad, diffusal, manta) or if you expect opportunities to pick off stragglers (ie if you have heroes like Zeus or Tide on your team that get lots of people low). The damage output it can do is stupid good. But again, it's only useful for 1v1's where not even creeps are around.
So yea, with every game being very different you should expect to have to vary your build based on what the amount of room you have to farm, whether the enemy comp can be expected to try to push hard early (necessitating items and skills that will help you fight and win those fights early), and whether you realistically think your comp can win a game that goes really late or not. But that should be a general idea of the thinking based on match conditions.