Unscrew the hinges that attach the gate to the gate post. Leave the hinges attached to the gate. Remove the portion of the gate latch that is attached to the gate post. Remove the gate. Place wooden blocks or bricks between the gate posts to temporarily raise the gate as you reinstall the hinges on the gate post. Position the gate on the blocks or bricks, centered between the gate posts.
Place a carpenter's level on the gate's top rail. Adjust the position of the gate until the rail is level. Push wooden shims between the gate and gate post to hold the gate in position. Hold the carpenter's level against the vertical stile of the gate frame. Adjust the position of the gate until the stile is plumb. Add more shims as necessary to hold the gate level and plumb.
Reinstall the hinges and latch on the gate post.
Unscrew the screws that fasten the infill planks or pickets onto the gate frame. If the planks are nailed to the frame, knock the planks out with a hammer, then remove the nails from the planks.
Reposition the infill planks, so their lower ends are aligned with the bottom of the lower gate-frame rail.
Nail or screw the repositioned planks to the frame.
Open the gate. Use the tip of a shovel to mark the ground, indicating the swing radius of the gate. If the gate won't fully open, estimate and mark the area under the opening gate.
Chop, dig, cut or pry out vegetation, roots, rocks or soil mounds from the soil in the gate's swing radius.
Smooth the soil, using a hoe or rake.