In this guide, you must farm as you can. Spectre is very weak hero in start, but has got good escape.
Spectre is REALLY hard hero fir first times, but really interesting. You don't know, will you win or not, because all depends on your skill. Don't try to feed your opponents in teamfights, it's just a big fissure in our future.

On first (1-20) phase, you need to farm. Take some ranged hero (not carry, support is best) to your lane, and farm. Kill as many creeps as you can, and use your ultimate on teamfights. Btw, your ultimate is great for escape some sudden problems.

On second phase, you should be more agressive, and kill weak enemies. When you wil have enough cool items, you're ready for show them, what is TRUE spectre.