Hand pull weeds when they first emerge. Pull them after a rain, when the soil underneath the pavers is slightly wet. Young plants come up easily. Do not leave the weeds lying on the pavers, especially if they have flowers. The dead flowers will produce more weeds. Instead, bag the weeds and discard them.
Buy a nonselective herbicide, such as one containing glyphosate. Mix it according to package directions.
Apply the herbicide with a sprayer to the weeds on a dry, windless day. Avoid spraying the herbicide on other plants because it will kill anything it touches. Follow all package directions and wear gloves, pants and closed shoes.