What is the next step in making over walls, after cleaning glue off?

Not enuf info. What do you plan on doing?? rehanging new paper?paint? tile? wood paneling? metal sheeting? Are the walls smooth enuf to paint? What are they made of drywall,plaster etc.? Are they damaged, may need to lightly sand to smooth,fill in holes,scratches,or skim coat depending on any damages with drywall compound or plaster; Painting--then sand smooth then primer then paint.

it depends on what you want to do on the wall- paint, new wallpaper, etc. we need more info

https://homeguides.sfgate.com/prepare-walls-paint-after-removing-wallpaper-38671.html

If you’re going to paint, I recommend using an oil based primer. Even a small amount of glue left over after cleaning will reactivate with a water based primer. Then the paint will peel.

Going to paint the walls

Prime with Kilz primer. Paint your color. Use a good bathroom paint. Has mildewcides and won't crack or peel.

When word of advice using the Kilz oil based primer make sure you have adequate ventilation I was with your professional painter and ended up with pleurisy of the lungs from The Kills toxic fumes if you don't have a window use a fan blowing out the door of the bathroom just paint small sections at a time it's highly toxic

Kilz is not toxic. The smell can linger of not covered. But painting over it will reduce or eliminate any odor.