If you’re going to jelq in the shower please avoid the shampoo and conditioner, the shampoo can dry out skin. Instead get your dick wet, turn your back to the shower, and apply Vaseline you can wetten it more for a slicker feel if you need.
I find palms down wet jelqs work better for me with girth at around 70-80% others prefer palms up, but to each is own.
Dry jelqs seem to lose pressure when going down the shaft so I have to split them into base to mid and mid to head. You might also want to apply a little bit of lube, no enough to make things slippery just to moisten your skin and hands so it doesn’t feel like an Indian rope burn.
You can still gain length and girth at the same time. Many people find stretches easier after jelqs or with jelqs between stretch sets.