I’ve experienced increasingly bad wifi performance on my Macbook Air over time. This has been accentuated further by me being somewhere with a lot of network lag. I did some research and the following suggestions made the wifi faster and more responsive with Mac OS 10.10.3 Yosemite.
1. Disable Bluetooth. I don’t use any wireless mice/keyboard/headsets, so Bluetooth doesn’t do anything for me.
2. Disable Facetime. Command+Space, Facetime. File > Preferences > [ ] Enable this account. I’ve never used Facetime, but from what I understand it’s Apple’s clone of Skype that only works with other Apple users.
3. Disable Handoff. System Preferences > General > [ ] Allow Handoff between this Mac and your iCloud devices. Handoff is Apple’s recent attempt to increase platform lock-in for those unfortunate souls who use non-Macbook Apple devices. Seemingly, it negatively affects network performance.
These three steps noticeably improved my wifi performance.
I, for one, look forward to the forthcoming release of Mac OS 10.11 El Capitan.