Keep floors dry. Clean up spills or wet spots immediately, using a dry mop or vacuum.
Put a rug over the slippery spot, or consider wall to wall carpeting if the whole floor is slippery.
Place mats at entryways, and buy mats that can withstand heavy traffic. Walkway mats can reduce slippage by providing a place where people can wipe their shoes and boots.
Consider replacing your flooring. Waxed flooring and finished wood can be the most slippery. Some tile material is billed as non-slippery and made for high-traffic areas. This will probably be your last resort. But if you have a floor surface that seems to be slick even if it not wet, you may need to install new flooring.