As with any painting or finishing project, preparation is so important.
Begin by covering your flooring with drop cloths or plastic. This will get messy!
If there are any major dents that require repair, fix those first using spackle or joint compound.
Minor surface imperfections, scratches and dents (less than ~1/4" deep) will be easily covered by the skim coating, but that hole where your couch leg nearly punctured the drywall (oops!) would be better filled before beginning.
Then, follow these 3 steps to prepare walls for a smooth texture:
Remove switch and outlet covers and any hardware from curtains or blinds, decor, etc.
Wash the wall with a small amount of mild detergent added to a bucket of water.
Dry the wall thoroughly with old towels or rags, making sure they are as lint-free as possible.