A closed transfer using CO2 to push from one vessel to the next is pretty standard. However I avoid using a secondary step whenever possible. Haven't used one in about 12 years actually.
Best way is not to transfer to secondary. Unless you're bulk aging a beer there's seldom any reason for secondary and any perceived benefit is outweighed by exposure to oxygen and the possibility of contamination. Most experienced homebrewers quit using secondaries several years back.
How to accomplish a closed transfer also depends a lot on the equipment being used. Without knowing what you have makes it hard to suggest a method.
Here is a diagram of a basic closed transfer system. Whatever vessels you use it is gas into #1/beer out of #1---> beer into #2/gas out of #2. The first and last ones are most important. You only want a small amount of pressure going into #1 and you want to relieve the pressure out of #2.
I transfer to bottle, but I wouldn't do it for secondary. When bottling using old school methods, you extend tubing into the very bottom of the bottling bucket trying as much as possible not to make any splashes. As with everything else, you sanitize the living hell out of everything that comes in contact with that beer too.