You may or may not be available immediately but laying out the groundwork for your job search is something you can do immediately. Hopefully, you are looking for a career not just a job.
Read the news in your field. Know who is doing what to whom. Know what's hot from what's not so hot. Make it a habit to read say the New York Times and the Wall Street Journal on a daily basis. Know what other fields are hot, especially those that are easy for you to get into given your training.
Find out which companies are active in your field and for which companies your specialty is likely to resonate. Schedule interviews with them, have off-line conversations with their reps at conferences and professional gatherings. Get some idea what matters to them so that when you are talking to them, you are talking in a way that's targeted to their interests. Having this information will help you do a better job of targeting your resumes and cover letters. I expect that you'll be sending hundreds of resumes and cover letters every six months or so, for a handful of responses.
Put your finger in the wind and get an estimate as to how favorable the economic conditions are going to be. If you expect the economy to suck by the time you graduate, you might have to look beyond the obvious companies for companies that are not in your field. I once advised a friend of mine and fellow chemical engineering grad student to go for IBM - The result was wonderful and beyond our expectations.
Think about key skills that might be valuable to a prospective employer but that take time to acquire. For example, being a hotshot Python programmer. It takes a year to be a very good Python programmer and guess what, you have one year to go before graduation time. Or you might think about taking advantage of the fact that you are still in school to take some classes in statistics that would give you an advantage if you go for jobs that require working with Big Data. Turn into an asset the fact that you still have one year to go before you graduate. Because when a prospective employer needs those skills, it needs them NOW and you have to have them NOW. In other words, this one year before you have to go is excellent timing for you to expand your skills set in a way that takes you into directions that are marketable for you.
Network like a maniac. Online and off-line. I joined my maximum limit of 55 LinkedIn groups. Have a strong online presence. And when you are networking, let everyone know of your interests, talk like someone they'd love to have as a collleague and let them know that you are looking. If you sense that they can't help you with that, ask them if you can run your resume and cover letter by them. Because you want the best resume and cover letter possible when it comes time to send them.
Networking is like going on a trip. You missing something if the only thing you care about is the destination i.e. get a job. You should also enjoy the trip i.e. talk to a whole bunch of people, learn from them and sometimes be surprised in some of the ways they could help you. When I was a grad chemical engineering student at Columbia, I made a point to acknowledge the cleaning staff as they were doing their job - I remember in particular this lady from Jamaica who let out that her son was about to start his career as an MD. You want to be good to everyone. Because you never know. Needless to say, building up your network takes time and speaking of time, you happen to be in the fortunate position that you have one year to go.
Networking is like friendship. Do not ask from those you network with for more than they could possibly give you. Yes, the only way you can get is by asking but always be careful to give them a gracious out. They may not be able to help you at this time but it's possible that they can help you at a later time. It takes time for you to determine who can do what for you.
If you are doing it right, you'll be awful busy between now and graduation with barely any time to breathe. If you find yourself with nothing to do but counting the days before you graduate, then you are doing it wrong. Very wrong. And unless you get very lucky, you'll pay the price for doing it very wrong.