Programs snatching focus after loading

Some programs take some time to open in OS X on a stressed older machine with a spinning hard disk. This is fine and understandable.

I would appreciate so much if someone would teach me how to instruct a programs that I launch to do so in the background?

Example: Suppose I am typing a Note, then I click Email to begin its launch and switch focus back to Notes and resume typing. I will be able to type for at least five but often upwards of 20 seconds, and at some unpredictable moment my typing will not show up on my Note but instead begin executing commands to whichever Mail window happens to be the last one I used last time.

How can I prevent loading applications from stealing focus after they are finished loading?

Any version of OS X, namely 10.9 and 10.10.