Mix the primer thoroughly. If you’re working inside, you might need to wear a ventilator. When applying the primer, use a paint roller and make long even strokes. You can also use a paint brush for any areas that are hard to reach with a roller. A handy tip when painting is to lay the paint off before it goes tacky for a finer finish. To do this, go over the surface very lightly with a roller that has very little paint on it. If you need to apply a second coat of primer, wait for the first coat to dry. Give the surface a light sand with 180 grit sandpaper, wipe off any dust, and then apply the second coat.