Begin from the most profitable business you earn and progress towards the least profitable to get the most from your assistants. After all businesses are available, get them automated using assistants. then, focus on getting the assistants for the best businesses first. However, do not complete all the Space Tourism ones first before moving to the other or you will lose money. Instead, increase them by a level, then restart using the same tactic.
Cat
Enter the office and occasionally a cat in a box will appear. Tap it several times to get some money.
Expanding
Spend gold to expand your business to different continents to increase profits and gain some experience points. Different continents will have different opportunities to expand. Consider starting in Africa or Europe because they are have smaller and less expensive regions. Wait until you have the enough assistants before spending your gold there.
Gold
Tap your portrait at the upper left corner then tap the "Buy Gold" icon at the menu. This will allow you to exchange your in-game money for gold. Each transaction will be more expensive than last. Until you reach a billion, the trades will be worth it. You can also get gold as you progress. Watch the advertising video that is available every ten minutes to earn one free gold. Spin the daily reward wheel to win a random amount of gold. Upgrade your businesses to get extra gold. Upgrade low paying businesses will give you the same amount of gold as you will get from reaching the same upgrade milestones for more expensive buildings.
Health and Productivity
Your Health and Productivity stats will drop over time. As they decrease, you will get less money. Keep both stats maxed by tapping the kitchen and water.
Skills
Skills give you extra experience points, which in turn is used to increase your character's level. However, you will get a lot of experience early from the achievements that are completed. Do not invest in skills until you have everything else set up.
Upgrades
So get the gold from the low paying businesses and use it to get assistants for the better paying ones.