Had this problem on a few of my earlier bikes. Various remedies: replace the whole assembly and lever; remove the pivot pin and put in an oversize one; re-bush the hole in the lever and replace the pivot pin (expensive and time-consuming). It has to get pretty bad before it actually affects the braking performance - often I just used to put up with it.
There are all different kinds of brake handles. You need to contact a motorcycle shop and give them the year and model.
Change the brake fluid - it goes bad over time. Bleed the brakes to remove any air in the system - air can enter the system if the master cylinder was to go low on brake fluid.
