I have found the best thing is baking soda and vinegar. Let it sit and flush with hot water. I actually try to do this once a month to keep them clear.
Also get a plumbers hook at the hardware store to help you fish out any gunk like hair that may be clogging it
Remove as much as possible with a snake or drain cleaning tool. Pour ½ cup baking soda then ½ cup white vinegar in the drain and cover, letting sit for 20 minutes. Boil water, remove cover, and pour water down the drain. You may have to repeat the process.
You can get this silly little plastic drain stick at any hardware store. It’s the bomb for everyday simple drain clogs esp in bathrooms. If you have a major clog you need a drain snake. This will slip around most drain stops and shower drains. The little ridges grab hair and soap scum build ups.
Not only will the baking soda/vinegar method unclog your drain, it will also help to get rid of drain gnats. Really works!!