For polyurethane bushings, silicone spray is OK, silicone grease (often sold as "dielectric grease") is even better and usually comes with the bushings.
For regular rubber bushings, I'd stick with the old mechanic's trick of hitting them with soapy water (and I mean SOAP, not dish detergent or shampoo), or else a powdered dry lubricant- usually called "graphite" but its mostly molybdenum disulfide.