OS X - Slow Wi-Fi? Hit it with your best shot

Problem 

Poor Wi-Fi performance?

Does you connection drop or look sluggish?

No fear, there's an easy quick for this.

Your problem could be caused by channel congestion.

If your Wi-Fi is setup on a channel already used by numerous wireless devices in your area, you may experience a poor performance and, at times, your connection might drop.

In layman's terms, a channel congestion is like having to go through a backed up highway over the rush hour. Too many cars (in our case, devices) out there.

OS X offers a quick and dirty fix for this problem, without needing to install any third-party tools.

Solution

 

Open Wireless Diagnostic (click+Alt on the Wi-Fi icon, or go to Applications/Utilities). 

Ignore the pop-up window (don't click Continue). Go to Window/Scan, instead.

In the next window, click Scan Now.

Click to enlarge

After the scan ends, you'll be shown the best channels (classified based on their frequency), i.e. the channels having the lowest interferences or, in other words, the channels where the fewest networks operate.

Click to enlarge

By switching your wireless network to one of your best channels, you can surely enjoy a much better performance.

You can improve your wireless router performance through other two methods, as well:

1. If your router supports multiple frequency bands, use the highest one. You can see my router supports both 2.4 and 5 GHz. I normally use 5 GHz.
2. Install any available firmware updates. Manufacturers usually release them to fix security vulnerabilities, but they can indirectly improve your router's performance, by solving software bugs.

6/21/2016 Update: 

This morning I could experience how useful this feature is.

After powering up my Mac, I couldn't access Wi-Fi and I had an error message saying "the.. network couldn't be joined". 

My 5 GHz network was gone.

I accessed my 2.4 GHZ network and ran Wireless Diagnostic as shown above.

After getting the best channels as previously explained, I accessed my router configuration page, switched my 5 GHz network to a different channel and, voilà, it was up and running again.

Troubleshooting time: two seconds.