SCBW as Businesses, Zerg vs Protoss context

You can think of Starcraft as a battle between two economies. Let me make a bad analogy. Terrible analogy. So, think of each race as a new business, and both businesses want to sell the same product. And people want this product. But they don't know which brand to buy from. So your bases are your establishments. You collect resources with employees, and invest those resources into other forms. Your fighting units are advertisements. So Starcraft is a battle of business establishments trying to advertise their new product. When you set up an expansion, you're setting up a new establishment in a district of the city, granting income.

Constant growth, resource management
For Zerg, larva can be considered a third resource aside from minerals and gas. When minerals and gas are kept low, it means you're spending effectively. Larva should also be spent effectively. When a hatchery is maxed with 3 larva and you don't build something with one of them before another Larva spawns, you're wasting Larva. So ideally you want to have your Hatcheries constantly producing something. If you don't have enough money and your Larva builds up, it means you don't have enough income (Drones) to support what you are building. If you have too much money, it means you don't have enough hatcheries to create an output to match your income. You have to balance the number of establishments you have with how much income you have.

Be flexible in your opening
An opening that appears aggressive does not have to continue playing aggressively. Opening pool first and making 8 Zerglings does not mean you have to try to attack. As long as your Zerglings are alive, they represent a threat that Protoss must account for. Zerglings deny scouting, so Protoss does not know if you're making more Zerglings or switching to a management type of game. If you see that Protoss is being greedy and skipping defense, you can punish that. If Protoss overcompensates on static defense, you can survive with a smaller force and safely tech, expand, or make more drones. Watching how the other business is spending money can help you decide how to spend your money.

Less static defense, more units
Static defense such as Sunken Colonies are useful against harass and as a first line of defense when your base is attacked unexpectedly. They are strong for their cost, but the major weakness is that they do not provide map control because they can't move. With 2 locations on the map to defend, Zerg would have to create enough static defense at both locations to stop the Protoss army. This means you've spent double the money that you had to. If you wanted to defend 3 locations with no army, you would have to spend 3 times the money that Protoss spent on fighting units. A Sunken Colony is 175 minerals, 50 (drone) + 75 (creep colony) +50 (sunken morph). 3 Sunken Colonies are more than the price of a Nexus. So when you rely purely on static defenses, Protoss can just not attack and expand all over the map.

Instead, if you spend money building an army, you can use the army to defend your base. Then both Protoss and Zerg should come out evenly. Buying signs that advertise your product will only cover a limited area of the city. It would take too much money to put up signs all around the city. Trying to put up signs all around the city will leave your opponent with much more funds to crush you with later on. Instead you hire people to go around the city advertising.

Upgrade unit armor and weapon and ability
Zealots have 1 armor with no upgrades. With +3 armor, Zealots have 4 armor total. Zerglings without attack upgrades do 5 damage. Zerglings without attack upgrades against Zealots with +3 armor do 1 damage to Zealot health per hit. Zealots have 100 hit points, so in this case it would take over 100 hits for a Zergling to kill a Zealot when counting in shields. Zerg armor against Protoss attack upgrades works similarly. When one side has +3 upgrades and the other side has none, the fight can easily become one sided. Upgrades are one way to make your advertisements more appealing or believeable.

Here are other things you can take advantage of that can help your business succeed or make it easier to manage.

Hotkey hatcheries and units
Hotkeys allow you to maintain production without having to move your screen back to the building every time you want to build something new. This allows you to direct your attention to more important things, such as the state of the game. You should hotkey each hatchery you have. Hotkeying units allows similar benefits. You can move all your units around the map easily, with greater manueverability.

Rally point to natural
A rally point tells the created unit where it should go when it spawns. A rally point can be set with the selected building by right clicking at the place where you want units to go. Normally each Hatchery's rally point is set to the same location on the map, usually in front of the natural expansion. Setting rally points is another thing that makes managing units easier: it allows you to not have to find each hatchery and group units from far apart.

Good Luck in making your business succeed!