Here some basic repair tips for woodwork you can do at home.
Splits or cracks
Mend lengthwise splits or cracks extending entirely through a piece by forcing glue into the crack, then putting on pressure to close it. Hold the pressure until the glue is dry.
Broken mortise joints
To repair broken mortise joints, butt-glue the broken ends jointly. Reinforce the joint using a screw or dowel long enough to get through at least 1 inch into the tenon member. Don't use this method to repair parts under great stress. Replace such parts altogether.
Dowels occasionally shrink and become loose on
1. Make a saw cut lengthwise over the shrunken end of dowel. Put in a small wedge in the cut, with the wide end of wedge protruding beyond the end of the dowel, and drive the dowel back into joint. This drives the wedge deeper into dowel, expanding it and causing the joint to tighten.
2. If wedging isn't practical because the parts can't be disassembled, anchor the loose dowel end in the joint using a smaller cross dowel or screw.
Repair cross breaks through splicing, or replace the whole piece. Splicing by scarf joint demands closely fitting all contact surfaces. Hand tools can be utilized with a simple jig, to ensure precise work. Using Jorgensen or C clamps, fasten the jig, guide, and pieces to be spliced to a workbench, and cut a bevel by slicing a hand plane, side down, on the edge of the jig base.