Intosport.com's YouTube channel is a great source for free Tennis skills and drills videos. Whether you are new to tennis or are just trying to get some ideas to take your tennis game up to the next level Intosports.com's YouTube channel is a place that you definitely want to visit and you might just want to subscribe to the channel. I know of no cost,other than your time, involved in watching this excellent Tennis instruction.
Here are a couple of examples of what you will find at Intosport's YouTube Tennis instruction channel:
This is a four and a half minute video discussing practice drills for doubles tactics: