We skim coated the walls in our dining room and the ceilings in the common areas to achieve a smooth look. The dining room was an orange peel texture and the ceilings were a knockdown texture. Both types of texture are pretty easy to fill with joint compound and smooth out with a magic squeegee and lots of sanding. More to come on the skim coating process in a future post.
Popcorn ceilings on the other hand could be miserable to skim coat. If the popcorn texture is not painted, the texture is pretty easy to remove. Simply spray the surface with water and scrape the texture off. You can attach a trash bag to this handy scraper to minimize clean up. If the popcorn texture is painted, you can follow the same process but expect it to take some grit and a bit more time.
PSA: popcorn ceilings may contain asbestos in homes built before The Clean Air Act in 1978. When inhaled, asbestos can cause lung cancer. It is inexpensive to sample a small area and send it to a testing facility. If there is asbestos, hire a professional or just leave it alone.