1. Time Management
One of my professors told me this in my first week and I've heard it repeatedly since – the biggest secret to succeeding in library school is to manage your time wisely. Being a compressed program makes this especially difficult as do the number of assignments we have – not all are intensive or hard but all do take up your time. I have no idea how some of the people in this program with families or part-time jobs do it. I bought a 12-month wall calendar which I've never done before and it's probably one of the wisest things I've done here.
2. (Speed) Reading
You will be asked to read A LOT in this program. Books, scholarly articles, journals, web sites, more scholarly articles, textbooks, handouts, magazines and did I mention scholarly articles? None of this will be reading for pleasure either so if you want to try to do that, add more reading (although it's almost a relief to do this type. I'm currently reading The Da Vinci Code and I think I'm enjoying it more than I would've in “real life” precisely because it's such a great “escape” novel – even if the actual writing sucks.) The other recurring piece of advice I got from past and current students when I started was to not even try to keep up with the reading assignments – it's “unpossible” as Ralph Wiggum would say. This was also wise advice.
3. Reading In General
This one seems obvious but you should probably be a bookish-type who does a fair bit of reading already if you choose to come to library school. I don't know – maybe that's not an absolute requirement (or it's more of a requirement if you're going into public libraries?) but I just don't get how anyone could come to library school and not consider themself a reader and/or book lover. That'd be like going to engineering school and saying you don't like bridges. (Are jokes about engineers building bridges universal or is that a University of Regina thing?) As well as reading lots, you should probably read widely as well – fiction, non-fiction, genre fiction, etc.
4. Interpersonal Skills
This is important anywhere – school, work, family – but being able to get along with various types of people is especially important in library school. Contrary to stereotypes, this place isn't filled with bookworm introverts – for the most part, people are pretty balanced and well-adjusted. But it does range from ultra-introverts to massive extroverts so being able to get along with all types will definitely help you out – in your everyday studies but especially when you're thrown into random groups and have to work on projects together.
5. Public Speaking
This one's important enough that I think they should probably do a brief session (one afternoon?) during the first week of library school to help people who maybe don't have a lot of experience doing public speaking to learn the basics. We don't do a huge amount (probably 1-2 things per class depending on which classes you're in) but it's something that's very important, not only in library school but beyond. And since it's people's number one fear, having a grounding in public speaking would be a big help rather than being thrown in the deep end which is what seems to happen now.
6. Computer Usage
This one is probably obvious as well but you should have at least a basic familiarity with computers and computer programs and probably more than that. This is a point of contention in library schools – the push-pull between how things have always been done and librarians who want to be on the cutting edge. (One publisher I know referred to “chip-head” librarians who are embracing any and all new technologies in an attempt to fundamentally change the stereotype of their profession as a bad thing that's getting worse about the current library system. Er, guilty as charged! 
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7. Typing
Sort of related to the last point, you should probably be a better than average typer if you come to library school. I mean, all of your five or six weekly assignments will still get done eventually if you're a two-finger typer but you just save yourself so much time by being able to type quickly.
8. Stress Management
Because of how busy this program is, dealing with the stress of assignments – readings, group presentations, essays, projects – can be a challenge at times. Apparently exercise and a healthy diet are good ways to do this; drinking massive quantities of beer and eating pizza six days a week is not so good.
9. Photocopying
Take the time to learn your way around the photocopiers in the GRC when you first get here as you'll be spending a lot of time (and money!) with them. Most people don't buy the textbooks and because of the twisted world of Canadian copyright law (it's okay for students to photocopy individual articles/textbook chapters for personal use but not okay for a prof to scan that chapter and distribute it electronically to their class for the students to print out themselves) so endless photocopying it is. Don't get me started on how idiotic this is.
10. Perspective
This is library school. At the same time that it's one of the most important things you can choose to do in society (in my completely biased opinion), it's also not rocket surgery. No one dies here, no one goes to jail, I don't think anyone hardly even gets kicked out. Unless you're applying to do a PhD, whether you got 76% or 86% on your assignment doesn't matter. In fact, no one will likely ever see the assignment but you and the prof. And let's be honest – we know that some profs aren't reading our works that closely either and the marks are about “artistic impression” and “technical merit” as much as anything. One prof admits as much saying “I don't know the difference between an 76% and a 78%. But I do know the difference between a B+ and a B-” which makes sense to me.
Bonus Link of the Day: Right before I came to Grad school, there was a thread on “How To Live With A Busy Grad Student” on AskMetaFilter that had some good tips, especially for those of us with partners/spouses/families.
