From Liquipedia Starcraft 2 Wiki
The Queen injects 4 Larva eggs into a Hatchery which after 40 seconds, hatch and 4 Larvae are ready to be used at the targeted Hatchery. Up to 19 Larvae per Hatchery can be spawned. If a Hatchery has 3 or more Larvae, it will not naturally create more.
Spawn Larva is the most powerful ability at the Queen's disposal. At every possible chance, the Queen's energy should be used to spawn additional Larva at a particular Hatchery. One Queen will recover enough energy to constantly spawn Larva at one Hatchery. This ability increases the ability of Zerg to produce any type of unit, so the Zerg no longer have to get multiple Hatcheries. As a general rule of thumb, each base the Zerg obtains can support one Hatchery with a Queen and its Spawn Larva ability.
When opening with Zerglings it is especially important to be using Spawn Larva at every available opportunity. The low cost of Zerglings and Drones means Larvae are used up very quickly. Missing even a single Spawn Larva while building primarily Zerglings and Drones can result in a stiff halt in production.
This spell can also be used on allied Hatcheries. For example, on team maps with close starting positions, one zerg can pursue Lair tech right after the Spawning Pool, while his team mate transfers a Queen (after casting spawn larva on her "home") over. This is usually followed by a Vespene donation as soon as e.g. Mutalisks become available.
There are several methods for injecting Larvae across all your Hatcheries, try them all and find the one which suits your personal taste, or create your own.
 Backspace Method
- Assign all Queens to one hotkey
- Hit the hotkey for all Queens
- While holding down (right-side) alternate between:
- Hit to center your next base on the screen.
- Click center of screen.
- If you have as many Queens as you do Hatcheries, using this technique can Spawn Larva at 5 Hatcheries in less than a second.
- You don't need more than one control group.
- It can be difficult to master.
- You have to change your current view .
- You have to move your hand from the left side of the keyboard.
Tip: You can change the hotkey for cycling through your bases fromto something that is easier to reach. Some people use
 55v Method
- Assign each Queen you control to a different hotkey. ( through , for instance)
- Hit and again to center the screen on your first Queen
- Inject Larva
- Repeat for through
- It's easy to do.
- Having a separate hotkey for each Queen can be useful for base defense or laying down Creep Tumors
- You have to change your current view.
- You may have to move your hand from the left side of the keyboard if you have many bases and queens.
- You need a lot of control groups.
- It can be difficult to do when having more than 4-5 Hatcheries / Lairs / Hives.
 Individual Hatchery Method
This method is used by most Korean pros.
- Assign each Hatchery to its own hotkey
- Double-tap the hotkey for a hatchery to jump to it
- Manually select Queen and inject
- Repeat for other Hatcheries
- Allows you to monitor the progress of injects easily because you can go through the control groups to see how far the injection is from completion, therefore it's easier not to miss injects even when your hatcheries are not synchronized
- Having each Hatchery on its own hotkey has various advantages such as being able to easily produce units at a Hatchery that's getting attacked for shorter reinforcement paths or setting separate rally points for Hatcheries
- Takes a long time.
- Takes up many control groups.
Tip: You should still use an extra control group for all your Hatcheries for easier production.
 Minimap Method
- Assign all Queens to one hotkey.
- Hit the hotkey for all Queens
- Hit minimap over each Hatchery you wish to inject. and left click on the
- Queens will inject the Hatcheries closest to themselves so don't worry about them running halfway across the map to inject.
- You don't need to change your current view.
- You don't need too many control groups.
- You don't need to take your hand off the left side of the keyboard.
- Takes some time.
- You can easily misclick on the minimap.
- Backspace method explained: 
 Patch Changes
|Patch 9 (version 0.11.0.15097)|