Begin by opening up your image, and making whatever lighting, saturation, etc. changes you would like to it. Also go ahead and resize the photo to whatever size you would like.
Make sure that you have selected the background image on the bottom right-hand corner in the “Layers” menu, since that is the layer we will be adjusting.
Then go to the upper menu bar, select Filter > Noise > Reduce Noise.
And this little box will pop up. I often drag it over to the side a bit so that I can see how the original image changes while I play with adjustments. (That is, assuming I have the “preview” button checked.)
My main priorities are to have “Strength” way up high (usually on 9), “Preserve Details” pretty low (usually around 10-20), “Reduce Color Noise” way-hay-hay down low (usually around 1-5, or else your colors will fade). I pretty much leave those three options set and rarely change them.