re: About to take on more responsibility at work, best ways to approach a raise...

Get an elevator speech ready. "Big Boss, I'm happy as all get out to be taking on the additional responsibilities. You will not regret your decision to let me fill the shoes left by Little Boss. I do feel, sincerely, that I am due a salary adjustment at this time, and later when I am fully qualified. Please give this your consideration. I look forward to our challenges ahead."

This happened to me, and I did not prepare or discuss with the Big Boss. When I brought it up later, he said he was waiting on me to show confidence!

If you don't ask, you don't receive.