My gf's Nexus 7 (2012) tablet recently was updated to Android 5.0 Lollipop, and the update has made it really slow and laggy. In the course of looking for a fix, I came upon a couple suggestions that should make all Android devices feel slicker. I did this on my LG G2 with good results.
First up, you need to enable Developer Options in your phone's settings. The exact method for doing this varies by device, but it's always in the Settings>About>Build Number section. (Build Number is sometimes buried a little bit farther. More info on variations here).
Once you find the Build Number, start tapping on it. It will pop up something that says "you are __ steps away from becoming a developer."
Keep tapping until you get a "You are now a developer!" popup, then hit the back button to go back to your main settings menu. There should now be a new entry for Developer Options. Scroll about 2/3 of the way down until you see some settings about animations:
By default, each of those will say Animation Scale 1x. Tap on each one, which will give you the option to disable those animations entirely, or make them faster. I like window transition animations myself, so I changed each of these to Animation Scale .5x which makes the transitions speedier.
Below these animation options, you'll have a check-box for Force GPU rendering. Check this box. It might eat a little more battery but it will make your phone overall feel a lot smoother and less hiccup-y.
And that's it! Enjoy your now much smoother feeling Android device!