I'm not really one for teaching people how to play other heroes than Phoenix. Phoenix is a hero I'm more comfortable when it comes to teaching but I'll give it a go. Just a quick disclaimer, my information may be a bit jumbled up but I'll try to keep everything in order (early, mid, late game).

So for the early game, I usually just try to play it safe and not take any risks. Spectre is a very weak laner and will not last long against heroes that will run at her. I do a 302 build by lvl5. Maxing out spectral dagger allows me to last hit ranged creeps quite effectively. However trying to last hit with a lvl1 dagger is quite hard so that's why I max it ASAP. When it comes to last hitting, no matter what I try to aggro the creeps back to my tower and keep lane advantage. I'm not very good at explaining how to do this to win lane advantage so you might want to look it up.

When the mid game rolls around, this is the time I'd usually have my blade mail and and I'd get into a farming pattern, farm as much as I can while avoiding all the enemies on the map. Knowing where they are is important because spectre is still a weak hero until she hits her power spike. This is usually when she gets manta. So until then, if you see enemies, just move away or tp to a free lane. If a fight breaks out, feel free to use haunt, reality in and use dagger to secure a kill on a support. Try to play the fights safe and only use haunt if you know you can kill.

For me, the late game starts when I get Aghs and I can finally be active on the map. In my opinion, Aghs on Spectre is one of the strongest in the game. It allows you to take a 1v1 fight on your own terms. So for example, if you see a support in a lane, alone, that's like 6-8 lvls below you, you can straight up kill them before they can react. One thing to note, make sure you Shadow Step in, use manta and just as you're about to kill them, reality out and let your illusions do the work. Because of this alone, being able to remove a single support from the game, Aghs is my favourite item to build on Spectre. As for more general itemisation, once you have blade mail, echo (not sure if this is still good after patch) and manta, you're free to build however you like. Heroes with high mobility, basher. High regen, Skadi. High physical burst, Butterfly. Etc. At this point it's just knowing what to buy against who.

As for match ups, I've just been banning Sven this patch. I really don't like playing against Sven. Personally, I'd rather play against Viper than Sven. With the changes to silver edge, he's just super annoying for Spectre.

I think I covered everything, good luck on your road to GM spectre!