Spackling is not a very strong compound and is only meant to fill in small holes made by nails and screws. Put the spackling in small spaces only, and only apply a little of it to the wall.
Wait for the spackling to dry, according to the manufacturer's instructions on the can. Sand it down with fine sand paper so that it is flush with the wall. Any ridges or uneven areas on the wall will be visible through the paint after its been applied.
Primer is a coating of white paint that provides a clean, white surface for your paint. Primer should be put on the walls first in order to prevent any discoloration between the spackling and the other wall color from showing through the final coats of paint.
Paint multiple coats of paint over the primer on the walls. This is especially important in cases where the paint you are applying is very dark, such as in the case of a dark red. Dark red paint is mixed into a transparent base rather than a white base, which means that the paint sometimes takes many coats to paint evenly. Apply two coats of paint, then wait for it to dry, and check the walls for uneven patches or blotches. If the paint looks blotchy, you'll need to apply another coat.