Apply a suitable amount of lubricant to the toy and spread it evenly over the surface. You can apply the lubricant straight from the bottle, or put some on your hand first and then spread it onto the toy.
Always use a lubricant that's suitable for your toy's material. Not every lubricant is safe to use with every type of sex toy.
For example, a silicone-based lubricant can react with some silicone toys, which may damage the material or make it sticky. If in doubt, it's best to go for a water-based lubricant.