To repair drywall dents and tiny holes:

 

• Fill dents and tiny holes with lightweight spackle using your finger or a putty knife.  
• Make sure the spackle completely fills the dent or hole and is level with the rest of the undamaged wall. 
• Allow the spackle to dry for 15 to 30 minutes or the time recommended by the manufacturer. 
• Once dry, use a fine-grit sandpaper to sand the area smooth.  
• Brush away any debris and touch up the paint. 

To repair drywall cracks:

• Widen the crack with a utility knife and brush away dust.  
• Fill the widened crack with lightweight spackle using a putty knife. 
• Apply a thin coat of spackle over the entire area. Smooth it with a putty knife. 
• Allow the spackle to dry for 15 to 30 minutes or the time recommended by the manufacturer. 
• Once dry, sand the area smooth.  
• Brush away any debris and touch up the paint.  
• If the crack is wider than 1/2-inch, cover it with self-adhesive fiberglass drywall tape. 
• Use a putty knife to spread joint compound over the drywall tape.  
• Allow the joint compound to dry thoroughly as recommended by the manufacturer, then sand it smooth. 
• If needed, apply another thin layer of joint compound and sand it again when dry.  
• Touch up the wall paint. 

To repair popped nail heads:

• If you notice a popped nail head, the nail has come loose from the wall stud. Reattach the drywall to the wall stud using a drywall screw.  
• Drive the drywall screw into the wall about 1 to 2 inches above the popped nail head. Sink the screw head just below the drywall’s surface. 
• Hammer the popped nail head back into the wall with a rubber mallet, being careful not to damage more drywall. 
• Cover the sunken screw and the nail head with spackle.  
• Allow the spackle to dry, then sand it smooth.  
• Touch up the wall paint. 

(From homedepot.com)