Level 20 Beta Build from Zephan over at Warcraft Tavern.

For our early Warlock talents, we have a bunch of great options. Wands now scale with Spell Power, making them a great replacement for Shadow Bolt: they deal nearly equal damage, or more with a good wand, at no mana cost. As such, we won't go into Destruction talents much, since they aren't that great at the current level cap.

The two most notable talents are:

• Suppression: gives us Hit chance across all spells and reduces our threat. With 4 points, you are hit-capped (the full 100%, goodbye Classic's 1% inherent miss chance!) against same-level targets.
• Improved Corruption: makes the spell instant cast and boosts its damage.

If you have a bonus talent point from the legacy talent system, you could even grab

You can arguably take other talents instead, such as:

• Demonic Embrace if you are Undead and want to deal more damage with Touch of the Grave.
• Unholy Power to buff your pets' damage, very impactful if you have a Sayaad at level 20.
• Improved Life Tap or Soul Harvesting if you are struggling with mana.

Source: https://www.warcrafttavern.com/forever/guides/warlock/

Looks like the wands scaling with Spell Power was changed in the new beta update, so it's back to good ol' Shadow Bolt!

Yea, sadly the wands have been nerfed. Fair, though, they were punching way above their weight. I'd just DoT stuff up and wand it down before it got to me, heh.

Rushing improve corruption definitely seems like the way to go, it feels like a big powerboost when you max it out. The extra hit chance is super useful as well, as DoTs are investments with little to no early payoff and so having to recast them on a miss really bogs you down.

Thankfully I've had no mana issues once you get over that early first few lv hump.