Just a quick guide here. Nothing fancy. I may improve it later on.

Long story short: DEQE...(waitforit)D.

Tier 1:
Subtlety is in the good spot for early and late game retribution. Not a must.

Tier 2&3:
Hemorrhage + slice and dice Strong synergy. Core build.

Tier 4:
Keep Cloak of shadows on sight as you might need it to survive in certains situations. If you feel comfortable with smoke bomb just go for it, is also a good choice.

Tier 5:
When playing among heavy hp teammates Death from above is a good gap closer for instant damage, use it for mobility (escape or finishing) not as combat opener. Elusiveness is also a great option in this context. However is an imperative to go for one of the two support options if tankiness is not one of the strengths in your team.

Tier 6:
Seal fate is the end game combo you are seeking for this build. Now D+E+Q+E+(stay till debuff**)+D everywhere.

**You can leave earlier Qu'ing away in order to avoid damage. Killing here is not the main target. Just harassment.

Tier 7:
Free pick.
Nightslayer is nice here by bringing early cloaking to the combo. Enveloping shadows is awesome too if you hadn't picked smoke bomb. However you can go for cold blood if you're feeling damage thirsty.

The synergy here is to open with Deqe (Deqqe below tier 6) trying to place it in the correct time and spot avoiding damage and escaping after even without the kill. Just to apply pressure and making trade wins.

A good Deqe requires a really little amount of time and applies a great amount of damage, so Slice&Go.

That's it for this Valeera guide. There is a lot of things left to be a good how to play Valeera guide. They probably a lot of wrong things too. The point here is add variety on builds and have fun playing.
Everything else you may already know.