Depending of the size and nature of the malfunction, repairing a wooden gate is a simple job that doesn't require an expert or even an assistant. Gates have three primary components: the frame, infill planks and articulating hardware. You can do minor repairs such as replacing infill planks without removing the gate. Major repairs such as fortifying the frame typically require removal of the gate from the gate post. Once you remove the gate, you can refurbish the entire gate.
Close the gate. Wedge scrap lumber under the gate to prevent stress on the hinges as you remove it from the gate post. Using a drill and driving bit, unscrew the hinges from the gatepost. Place the gate on a flat surface, infill-side-down.
Inspect the gate to diagnose problems with the infill, frame or hinges. Beginning with the frame, use a carpenter's square to determine if the corners are square. If the gate is significantly warped, you might need to remove nails or screws in the frame before realigning the corner joints. If the corners are only slightly out of square, realign the joints by tapping the opposite ends of the framing members with a hammer. Once the joints are square, lay a flat corner iron diagonally across each corner. Use wood screws to attach the irons to the frame. Reinforce each joint with two screws through each corner.
Turn the gate over. Remove any broken or rotten infill planks or pickets. Measure, mark and cut new infill planks as needed. Reposition the replacement planks on the frame so they are parallel to adjacent planks and spaced evenly. Screw the planks to the frame with two screws in each end.
Tighten the screws that attach the hinge to the gate if they are loose. If the screw holes have become stripped, you can wobble the hinges to remove the hinges. At this point, you should reinforce the screw holes in both the gate and the gate post.
Pour a teaspoon or so of wood glue onto a saucer. Dip about half the length of a toothpick in the glue. Push the glued end of the toothpick into the screw hole as far as it will go. Continue gluing and inserting toothpicks in the screw holes on the gate and gatepost until the holes are tightly filled. Allow the glue to dry according to the manufacturer's directions. Once the glue has dried, use your fingers to snap off the protruding ends of the toothpicks.
Reinstall the hinges on the gate, using new screws. Position the gate between the gateposts, resting it on scrap lumber to support it while you reinstall the hinges. Realign the hinges with the reinforced screw holes. Securely affix the hinges to the gate post, using new screws.
Screws used to reinforce the corners should be long enough to hold the joint securely, with the tip of the screw at least 1 inch past the joint.