Just like floorboards, staircase creaks are usually caused by the rubbing together of two pieces of timber. Repairs don't require any specialist tools and as with most diy jobs - just a little patience.
Locate the creaking joints by removing any stair covering and stepping on each step in different places across the tread. You may be able to carry out repairs from the underside of the stairs if it is not covered with plaster.
Stair riser and tread joints
Loose tongue and groove joints between the rise and the front of the tread can be repaired by squeezing wood glue into the gap and forcing it along the joint with a fine-bladed knife.
If you can work from the back, add a triangular-shaped glue block to bond the tread and riser together.
If you have to work from the front, drill and countersink at least three screws into edge of the tread, into the top of the riser to force the pieces together.
Loose housing joints
Sometimes treads and risers will shrink and become loose within the housing joints cut into the sides of the staircase.
If you can get to the back of the stairs, you'll see that each rise and tread is held in its housing with a timber wedge. If the stair is creaking, the wedge may have become loose. Remove the wedges and chip away any old glue and debris.
Remember to wear safety goggles to protect your eyes.
Apply wood adhesive to the housing recess and, having cut some new wedges which are the same size as the old ones, tap these in with a hammer to tighten the joint.
If you have to work from the front, drill and countersink holes along the edge of the loose part and screw into the sides of the stairs at an angle. Hide the screwheads with filler.