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I gave my first GMAT Mock a week before without any preparation and score 670.
If you're new to the GMAT, the gmatclub study plan post could be helpful (it mentions a variety of resources, for example). Fair to say including official questions/official mocks into a prep path would be a solid choice. E-versions of different official-guides are available, too. If there are resources you're interested in and want to check out, leveraging their trial periods could be helpful.