The answer does depend on what type of levers you have. If they are Loveland levers (which have a brass base and a black handle), then loosening the nut on each lever handle should do the trick. We've never needed to lubricate the Loveland levers.
If you have Robinson levers, which are all brass, then it's a bit more complicated. The handles are riveted to the bases and aren't really adjustable the way the Lovelands are. Sometimes lubricating them works for a while, but usually people end up replacing them with new Robinson levers.