While some problems with OS X will be very distinct, sometimes after upgrading there may be a few nondescript problems that occur, even if it’s something as small as the mouse not tracking as well, or the system having odd hiccups of slowness, or perhaps a visual artifact or two on a Web page. If odd little problems are happening to you after upgrading to OS X Yosemite, then while at times they may indicate a larger problem or bug, in most cases they can be rectified with a few quick and common fixes.
1. Ensure you have updated all third-party software.
First and foremost, any OS upgrade will bring changes to how third-party software is run, so be sure to visit the App Store and apply any software updates present there. Ensure all other third-party software you use has been updated as well, especially if it has components that run in the background.
2. Quit and relaunch programs
OS X will save the state of applications you have open, even after upgrading OS X. In doing so, the configuration the program was using in Mavericks or earlier will be loaded after Yosemite is installed. Most of the time the OS’s services and the applications you are running will work together just fine, but sometime a program or two will load in an odd way. Unless there is a bug with the program that is the cause for the issue at hand, often the easiest fix here is to simply quit and relaunch the program. This often is a quick fix for odd visual artifacts such as window elements being drawn in unexpected places, or being slow to respond to your input.
3. Restart your system
Applying the idea of quitting and relaunching to the entire system can clear a loaded configuration error or two that is causing the problem at hand. OS X uses numerous caches to store frequently used configurations for quick access, and a quick reboot should ensure these are properly loaded.
As a quick maintenance routine, you can restart your Mac into Safe Mode by holding the Shift key down when you hear the boot chimes. This will load only a basic configuration of OS X (so the system will run slow and with limited features), but will also do things like check your disk for errors and clear some routine caches the system creates and uses. After booting successfully into Safe Mode, restart your Mac normally and see if it performs better.
5. Reset your Mac’s PRAM
PRAM variables are hardware-based settings to help manage your system when the operating system is not loaded. In addition to classic uses such as the setting for the primary boot drive, some of Apple’s various services such as iCloud use PRAM variables. If damaged, settings in the PRAM can cause odd problems such as relatively long boot times, so you can try resetting your PRAM so default and new settings are loaded into it. To do this, reboot your system and hold down the Option-Command-P-R keys when you hear the boot chimes. Hold them until the system resets and sounds the boot chimes again, after which you can release them to allow the system to boot normally. You can read more about resetting the PRAM here.
6. Disable and re-enable relevant settings
If the problem at hand appears to be with a specific setting, such as the mouse tracking behavior seeming too fast, then try going to the relevant system preferences and toggle some of the settings there. Sometimes this is enough to spur a rogue setting or two back to an expected value so it will work properly. In this realm, consider things like turning Wifi off and back on, or
7. Quit menu extras and background apps
If you have a number of menu extras and background apps installed on your Mac, then consider quitting them all for now. These can include system monitors, security software, online storage managers (e.g., Dropbox or Mediafire), and any other third-party software that puts a small menu to the right-hand side of the menu bar. If you require some of this software, then check with the developer for an update, or try launching them one-at-a-time to see if any specifically is contributing to the problem at hand.
Overall, for most small and nondescript problems you might encounter after upgrading to OS X Yosemite, they should iron themselves out with basic use, so after upgrading, try some of these suggestions several times to see if the problem goes away. If the problems continue after performing these steps, then you will need to investigate them further.