Four Ways to Use Other People's Work

"What if we did something like The Most Interesting Man In The World?"
How many times do you hear this kind of thing when you're concepting? How many times do you say it yourself? As a starting place, or when you get stuck in a rut, or because you're searching for the formula for great work, you start with great work and try to go from there. 
All creative work is somewhat derivative, but this technique guarantees it. It's okay to be motivated by great advertising. It's good to know what great work is out there. But your job is to do something different. Something that's right for the brand you're working on. Ideally something that doesn't even feel like advertising. That's hard to do when you start with advertising. 

Most advertisers get their inspiration from looking at other advertisements. It’s no wonder they all look the same... If you constantly search in the same treasure box, you’ll constantly find the same treasure. Look elsewhere and you’ll find something new.
                                                                    -Paul Arden

Using advertising as inspiration for creating advertising is just recirculating stale air. That said, there are ways you can use other advertising to improve your own game. Here are a few thoughts:
1) Take it apart. Put it back together. When you find an ad you like, don't stop at "Hey, that's cool." Study it. Figure out why it works. Dissect it. What decisions were made and why? Try to retrace how the idea may have come about.
2) Write the strategy for the ad. What insight was the jumping-off point for the ad? What questions did the team ask? Who is the ad speaking to? What's the main takeaway? What story are they telling? See if you can articulate all the elements that would make up the strategic brief for the ad.
3) Present the ad. See if you can present the concept for the ad. Make a compelling case for why it's good. Present it with drama and conviction. In my scriptwriting class, I have students present the concept for a tv spot they love, then we watch the actual spot and critique how well their presentation captured the essence of the real thing. (I'll be honest, I usually imagine the creative presentation of an ad when I see some hacky piece of crap on tv, wondering how someone could actually present that idea as if it's good, but it's probably more useful to imagine yourself doing it with something you like).
4) Critique the idea. This is good for when you're sitting in a long internal creative meeting and listening to other teams present work (or when you're in class listening to another student present). Take that opportunity to formulate an opinion. Even if nobody asks what you think, you can practice creative directing. What ideas do you like? How would you make them better? How would you deliver your feedback? Compare your direction to the CD's. Giving direction on the fly is tough, so it's worth practicing a bit, even if just in your head. Plus it keeps you engaged in the meeting and it's probably more beneficial than doodling caricatures of the account folks.