Your guest rating is how well you're attracting customers.
You can see what your guests want by hovering over the Main Gate and pulling LT. If they want entertainment, add some entertainment concessions or upgrade the ones you have. If they want animal variety, add some variety with your animals. Mini exhibits are good for this because they aren't expensive.
Keeping prices low or reasonable is another way to attract customers. If your animals breed, particularly if they breed a variant, that's good for customers.
And there's always the most reliable way to gain guest rating: advertising. Use the Research Tree at the Main Gate to upgrade your advertising, and blast away with whatever your level will allow. You can even crank up the prices during an aggressive ad campaign.
10,000 isn't really that much. Keep your animals and guests happy and used ad campaigns!