Buggy Yosemite? Fix it quick for good!

The 10.10.2 update hasn't yet solved numerous OS X Yosemite bugs.

Here are some quick solutions to the most common problems:

1. Slow performance: especially for older Macs, Yosemite's new features can slow down your system. Selecting Reduce Transparency (System Preferences/Accessibility/Display) is a solution but makes OS X look awful. The dark look is a good alternative but the Google Drive icon in the menu bar becomes invisible. A workaround for this is here. You can disable the Dashboard, too, from System Preferences/Mission Control or from Terminal (defaults write com.apple.dashboard mcx-disabled -boolean YES && killall Dock). 
2.  Wi-Fi problems: Some users have complained about Wi-Fi issues, which seem to especially affect who upgraded from a previous version, rather than fresh installs. The most credited solution suggests to trash certain preference files related to wireless networks from /Library/Preferences/SystemConfiguration/ folder. If you're reluctant to mess up with system files, you can try an easier way.  Go to System Preferences/Network, remove your current network (by clicking the "– " button, with reference to the below image) and add it again manually ("+" button). You can also run Wireless Diagnostics to understand what specific factors cause your problem. Wireless Diagnostics can be run by pressing ALT key while clicking the Wi-Fi icon or looking for "wireless" in Spotlight. For more details about this utility, check out MacOsX Mavericks- Wi-Fi keeps dropping? Here's why. Disabling "Wake from Network Access", from System Preferences/Energy Saver, can also be beneficial.  
3. Bluetooth problems: Bluetooth devices might intermittently lose connection for a while. Apple suggests to reset the PRAM (Parameter Random-access Memory) by pressing CMD/ALT/P/R at boot-up. In my experience, this can be due to interferences between the Wi-Fi and Bluetooth frequencies, and switching Wi-Fi channel can often solve it. 
4. Problems with Mail: Yosemite hasn't solved numerous issues, already present in previous versions, related to the interaction between Apple Mail and Gmail. After upgrading, Mail stopped working and, unlike what's been suggested in this page, removing and adding manually my account hasn't worked. The only effective solution is to tweak the security preferences in your Google+ profile to enable the "less secure applications". In other words, for Gmail to work with other third-party applications, you need to downsize its security level. For more details about it and other issues related to Apple Mail, check OS X 10.10 Yosemite issues - Bugs for all. Wake up, Apple!.