When speaking about preparing the garage floor. You need to keep the floor or the ground clean; free from dirt, oil and derbies because such things will make the bonding of the cement difficult. So try using a good detergent and a scrubber with stiff bristles to scrub away all the dirt. You many even give an acid wash to make the ground much cleaner. Give more attention, if you find any cracks when cleaning the floor. So try fixing those cracks before you make the concrete mixture. All cracks can be filled with epoxy paste which will dry faster and the excess can be scraped off. Make sure you always keep the ground free from dirt after cleaning. If you think there is any moisture in the garage ground, here is a small test that you can do. Cut a small piece of plastic sheeting; tape all the edges on the floor. If you find water collecting under the plastic sheet due to evaporation, then it shows that your garage floor contains moisture.
Once the garage » Read more: Painting and Preparing your Garage Floor