Collection development in 4 easy steps! (with music for my amusement)
Step 2: Know your surroundings. There might be a library out there that can afford to buy everything they want in the quantities that they need. I would love to work at that library. Unlimited budgets! Unlimited space! Yeah...not so much. Every library has to make choices, so help yourself out a little bit. Know what things are available in your community. If you have reciprocal borrowing with area libraries, that can be a great thing.
Step 3: Know your limits. Whenever people ask the wonderful question "How do you keep up with all the new things coming out?" I always give the same answer: "You're never caught up." This is the truth, and the earlier you embrace it, the better off you will be. This is a job where there is always something to do. Always. There are always new titles out tomorrow, next week, next month, next three months, next six months... There will always be a title that was out yesterday that flew under your radar. There is the unexpectedly announced title. Even if you manage to get caught up on all the upcoming titles, there is always the backlist. Oh, and make sure you got those things in every format suitable for your library. Did you get the large type? The CD? The Ebook? The downloadable audio?
This isn't meant to be discouraging or overwhelming. When it was told to me, it actually had the opposite effect. Relax. You'll do what you can do. I've seen people taking catalogs and things home to try and "catch up" but the next day, something else lands on their desk. Eventually, every collection development librarian I've ever known creates their own system for handling the amount of things they have to work through. You take big things, and you turn them into smaller, more manageable things. Maybe that means another person comes on board, maybe that means processes have to change...whatever. Knowing your limits saves your sanity, and it always saves you from making costly mistakes due to being stressed and frazzled. Relax. You got this.
Step 4: Learn what else you don't know. There are lots of libraries and librarians doing collection development, and most of them do it differently. Talk to all of them. Go to presentations, in person and online. Webinars make learning much more affordable (and timely) than attending a big conference once or twice a year. Follow them on Twitter, Tumblr, read their library blogs--hell, even listservs are still around. Join those too. See what others are doing, and learn how you can adapt what they're doing to your own situation. Do the same for authors, publishers, agents, anyone who works in the ecosystem of books/movies/music and games (or whatever your library is buying). Libraries are part of the larger ecosystem, and the more you know about the overall business, the better off you'll be.