Any surface that you are going to paint should be properly clean and free from debris and dust, otherwise there is no way the paint will stick no matter how may coats you apply. So before starting to paint the concrete garage floor, properly sweep and mop it. You may have to wash the floor to get rid of any grease stains that may have formed on the floor due to oil dripping from the engine. Use a mixture of degreasing solution and water to make things easier if the grease stains are too stubborn.
Image Courtesy: nuvogarage.com
Thoroughly vacuum the whole floor at least three times to clear away any debris that might have been left over. Just to be one the safe side, wipe clean the floor with a tack cloth after you are finished vacuuming it.
Image Courtesy: fishingnetwork.net
Before painting the floor, you may have to do some concrete patchwork. See if the garage floor is cracked in some areas of if there are holes in some places. Make sure you completely fill these cracks and holes by filling them with concrete patch compound before moving on to the next step.
Image Courtesy: concretenetwork.com
With a paint roller, apply a uniform coat of primer and allow it time to dry completely. Apply another layer of primer to provide a firm base for the paint to stick on. The second primer coat will increase adhesiveness between the floor and the paint layer.
Wash and clean the paint roller from the previous step or use a new one for this step. Apply two uniform coats of epoxy paint, letting the first coat completely dry before applying the second one.
Image Courtesy: epoxygaragefloornow.blogspot.com
Since it is the garage floor you are painting, it will have to go through a fair bit of wear and tear when you park your car in the garage. To increase the life of paint and to make sure it lasts for a longer duration of time, apply multiple coats of masonry sealer. Make sure you allow time for one coat to dry properly before applying the next sealer coat.