Your pruning shears will cut more efficiently if you clean the blades after each gardening session with a toothbrush dipped in paraffin, then wipe with a light lubricating oil.
To restore the cutting edge, take the shears apart by unscrewing the pivot nut and removing the pivot bolt. Sharpen by stroking a medium-grit oil-stone along the cutting edge of the blade. Move from the pivot end to the tip, matching the original bevel as closely as possible. Never hone the inside face of the blade, except to remove the burr left by sharpening. Then repeat the process with a fine-grit stone. Reassemble the shears carefully.