Until you get to Tier 2, you really don't have much opportunity to dictate the terms of play. While Scouting is so important for all races, it's soooo important for Zerg to scout constantly. From the start you'd want to know if your opponent is going to 2/3 gate, or proxy reaper/bunker, or early Hellion/Banshee... There are so many cheeses that others players can do to you, you'll need to know before deciding whether to fast expand or go 14 pool. Especially going into the mid-game, if you need to sacrifice overlords to scout, then do it because you have to know what they're doing.

As Ghavrel mentions, you want to constantly spread the creep, and spawn larvae on your hatcheries. Try to get used to those mechanics, you never want your queens sitting idle. Zerg require a lot of Macro, you want to always expand and saturated your mineral lines when you have the opportunity. When you're harassing, expand. When you're attacking, expand. If your opponent has 2 bases, you should have 3 or 4 expansions.