If you leave your iPad to charge over night you know it will be at 100 percent in the morning. In other situations you may want the charging to be as quick as possible.
The most important thing to get your iPads charged quickly, is to use the right charger.
You can use any of Apples iPhone or iPad chargers to charge any iPad or iPhone without risk of damaging anything. They do, however, charge them at different speeds. A 5 watt iPhone charger will charge most iPads very slowly. Use one of Apples 10 or 12 watt chargers for all iPads except the iPad Pro.
For the 12.9 inch iPad Pro the 12 watt Apple charger is not enough if you want to charge it as fast as possible. Then you should buy Apple's 29 watt USB-C charger along with the USB-C to lightning cable. They both are expensive, but they do charge the iPad Pro much faster.
Some wonder if you can charge other iPads with the 29 watt USB-C charger. According to Apple you can (It says "You can also use this cable with your Apple 29W, 61W, or 87W USB-C Power Adapter to charge your iOS device, and even take advantage of the fast-charging feature on the 12.9-inch iPad Pro." on the USB-C to Lightning cable description). I do and so far haven't had any problems.
Another thing to consider when you need to charge as fast as possible, is that you will get maximum speed if you turn the iPad off while you charge. Then it will not use any power for network traffic and background updates.
Use Apples accessories for charging, or at least MFI certified ones. Many uncertified accessories are of poor quality and may even damage your devices.