The liquid is usually due to one of two problems: adding too many "wet" veggies, which give off excess moisture, or adding too many liquid ingredients like soy sauce or sesame oil.
If you're using sturdy ingredients that can withstand being cooked down a little longer, simmer the liquid in your pan until the water evaporates and thickens up naturally.
If you've used delicate ingredients, such as shrimp, leafy greens, or vegetables like snow peas, you run the risk of wilting them if you let them simmer for too long.
You could also drain the excess liquid, but you'd drain away some of the seasonings, like the soy sauce, cooking wine, and sesame oil, and sacrifice the flavor.
Instead, pour some of the liquid into a bowl with a few teaspoons of cornstarch, and whisk it into a slurry. Add it back to the pan, and briefly simmer it to create a thick sauce.
To prevent sogginess, avoid using veggies with high water content, like zucchini, cucumber, celery, and bell peppers, or wait until the very end to throw these ingredients in.