Hyaluronic acid, because it's humectant, it should be applied to your skin while it's still damp. So, you have to cleanse your skin first. This ideally will happen say for example in the evening - take off all of your makeup, sunscreen, mascara out. Remove dirt, oil and I do a double cleanse. I use lots of face oils that nourish my skin. One of the best antiaging oils is plant-based bakuchiol, alternative to synthetic retinol. Learn more about them here: https://theplantmother.com/face-oil/. I start with an oil-based cleansing balm or cleansing oil, I ladder it to my face and around my eyes and my eyelashes to start to break up the mascara, the sunscreen, my own oils, pollutants that have settled on my face, pollens arrow allergens, etc. And then I hop into the shower and I rinse it off.
Then lather to my face a non-soap gentle cleanser. This helps to remove all of that very efficiently, the polyethylene glycol components of the cleansing oil or something similar. Marry that with the water and marry with the second cleanser and everything works just efficiently and smoothly comes off and doing it this way minimizes disruption to the skin barrier and helps with skin that is crepey.
And when I step out of the shower while my skin is still damp. This is when you want to immediately apply your hyaluronic acid serum to your face. You don't need a ton, just a small amount enough that you can feel a thin film to all surfaces that you're interested in using the product. So go ahead and apply it, you know you can apply it to your entire face or just a targeted areas and really what this is going to achieve its going to deliver some more focused hydration that can improve the appearance of fine lines and wrinkles, overall skin texture smoothness, just delivering a little bit of focused increased water binding.
So you might just be interested in improving hydration around your eyes and not for the rest of your face. You want to keep that serum and not run out of it as fast and as long as you're using it within the expiration date that is prudent, but you might just want to use it to focus on areas. Maybe you just want to improve some fine lines on your neck. Sample just use it where you want to and you can use it to your entire face you don't need a big glob, just enough that you feel a thin film on there.