Looking at ways to give your room a finished look? Maybe you could consider installing molding to hide those flaws.
Step by Step
Locate and lightly mark the wall studs. This can be done by rapping the wall with your knuckles or with a hammer to which a tap or thin padding has been attached. The sound of the wooden stud beneath the wall will be different from the hollow sound that the spaces between the studs will produce.
Once you have got the measurements of the height where each molding will go, cut it accordingly and apply the finish to the molding in the same order that you intend to install the pieces. For outside corners, use a power miter saw and for the inside corners you have the option to miter cut the pieces or cope them.
To do this, you need to place the molding so that the part that goes against the ceiling is flat against the bottom of the mitre box and the part that goes against the wall, should be flat against the side of the mitre box. Cut the pieces as mirrors to each other on 45 degree angles.
You would then need to pre-drill the molding at every wall stud and nail in place. In order to avoid denting the molding, it would be advisable to use a nail set to finish driving the nails home. If there is a span between two corners that are longer than the molding, make a scarf joint to slice two pieces. You can accomplish this by laying the molding with its back flat against the bottom of the bed of the power miter saw.
On one piece, cut through the face at 45 degrees, so that the edge of the cut is visible from the front and on the second piece, cut through the fact at 45 degrees so that the edge of the cut is hidden from the front. Basically, the joint should meet over a wall stud or at a point where it can be nailed.
You can then continue installing all the molding pieces and then touch up any raw edges with a coat of finish. You could use wood putty to hide the holes caused by the nails. In the case of crown molding, you might need to apply for a bead of caulk to close any possible gaps that appear where the molding meets the ceiling. Caulk can be used both to repair and seal while giving the required protection.
Molding with Corner Blocks
If you are planning to install molding with corner blocks, first find out how much molding you will need; count the number inside and outside corners in the room so that you will know how many blocks you would need.
Measure the distance between the first two corner blocks and put one end of the molding tight against one of the corner block. You can then put the other end over the other corner block and trace the edge of the corner block onto the back of the molding.
You can then take down the molding and cut it on the outside of the line to make it fit and then follow the above procedure of finding the studs in order to locate and mark the wall area and continue from there.