If your deck railing is loose or wobbly it is probably the result of a weak rail post connection to the deck frame.  If your rail posts are mounted to the interior of the frame you can remedy this by installing blocking around the post to trap the post in a pocket.  You can also install dek lock brackets to reinforce the rail posts.  These brackets are expensive but create a very solid connection.  If your railing posts are connected to the outside of the frame you can try to tighten the bolts and install blocking to the rim joist to stiffen the rail.  Ledger bolts with washers work better than carriage bolts because the washers provide a larger surface area to apply pressure to the posts.