If you are planning to write the GMAT after 1 year, I believe it's too early to start your preparation.
3 months is the recommended time. People who extend their prep phase more than three months tend to burn out and perform sub-optimally. However, you can start building your foundation in maths.
There's a book called "Quantum CAT." The book has a lot of solved problems and the theory coverage is also pretty good. It's very good for self study. Unfortunately, it's available only in India. You will have to get someone from India to ship it to you. Also, it costs only Rs. 550. Compared to other GMAT prep books, this book is dirt cheap.
Once you get that book, spend around 1 hr every day learning concepts, making notes and solving problems. Although you're spending only 1hr a day, if you do it consistently, these small increments will add up and you'll see a remarkable improvement in the long run.
Plus, studying only 1 hr per day will prevent you from burning out.
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From 650 to 710 to 750 - My Tryst With GMAT [Experience Thread]