For projects where i need a higher level of artistic skills than what i can currently pull of, i hire an artist or more (like an artist and a colorist).
Even if you go that route, knowing how to draw well enough to explain clearly to your artists the visual concepts you are aiming for can help a lot.
If you don't have the money for that yet, you can try to save up and set a budget to hire people. How hard or easy it will be will depend on your financial habits and situation. But if you are able to save some cash, you can stockpile enough to hire people.
If you decide to do the art yourself, you can practice and focus on different aspects. If you need a specific style sometimes a book that teaches how to reach such style can help wonders. Personally i recommend books that teach artistic principles.