First, launch Spotlight. For most people this is Command-Spacebar, but you may have set it to something else, I'm not the boss of you. In any case, when you get to Spotlight, start typing the name of the app you want to launch. If it appears at the top, like my example, just hit return and you're off to the races. Or, in this case, to Word:
Spotlight results in Yosemite.
You can also choose from the results using arrow keys or the mouse if you prefer. Here's where this tip pays off even further: If you do this often, then all you end up having to type is a single letter:
Launch apps by using a single letter. It's almost like having a psychic friend!
And this makes you even more efficient since your fingers don't have to leave the keyboard and you can already be typing away in the app you just launched. Thanks Michael!