Some take months to pore over every possible piece of information that might show up on the exam. That's a fatiguing way to go, though can lead to some useful learning--not just for the exam, but for social work practice. Or even cocktail party chatter. Not that social workers usually have time to go to cocktail parties.
Others, with greater faith in their test-taking ability (and/or luck), give it a week or two, read over material they know will show up on the exam (the Code of Ethics, for example), and go for it. That works for the breeze-through-school type. If you can pass the exam with a minimum fuss or bother, that's great--nice to be you!
Another approach is to not study at all, take the exam, either pass and celebrate or wait till the next exam period and go in with a solid idea of what the exam looks and feels like and just what's involved in the process. Of course, old exam items are retired, so if you try this, you won't see the same exam questions, but...you'll know more-or-less what to expect and what to focus your studying energies on. But you'll have also spent a bunch of extra money and possibly delayed getting licensed by six or more months!
Just like in Goldilocks--and the rest of life--there's a "just right" option to consider. The middle way. Not too much studying, not too little. Just right. That seems to be the preferred way to go for most social work exam preppers. Give it a month or two. Take practice exams to get a taste of what it's like to sit though a four-hour, 170-question test, review areas that you're weakest in...repeat. It's cheaper than taking the real exam (as long as you shop well). It's less of a gamble than studying just a little or not at all. And you'll probably learn some good stuff along the way.
Which of these is the best approach for you? Look at your test-taking history and your comfort with social work concepts and values. Think about what's going to help you arrive at the testing center feeling at ease. Scramble those all up, maybe flip a coin, or close your eyes and hit a date on the calendar. Book the exam, make whatever preparations you deem necessary...and liftoff. Go pass.
Good luck!