Rune Strike should be your first priority for using runic power, so it's easier for your rotation if you just macro rune strike into all your abilities, that way you will be spamming rune strike without any effort while you use your other abilities. Here's an example:
Another alternative, if you feel you want more control over when you're using RS, is binding your mouse wheel to RS and spinning the heck out of it while you want to spam it. This is useful if you want to makae sure for other stuff (interrupting, unholy blight, etc) but when tanking bosses you really want to use RS as your first priority most of the time, so macros are really effective.
/cast !Rune Strike