First challenge ‘have to’. The most common reason for registration is that customers are demanding it. If you can show your customers that you understand what matters to them and you have translated their needs into the way you manage your business, why should you need the Standard?
If you still think you ‘have to’, the first thing you should do is get to meet lots of assessors. Interview them on their interpretation of the Standard as it applies to your system. You need to select an assessor who will not be dogmatic about features of the Standard that can result in poor quality.
Use your own people. Don’t start by having them document what they currently do, start by looking at the organisation as a system. Lead them through check. Make changes to things that need changing. Put aside the Standard for the whole of this period. Consider, for your system, what (minimal) control you need. Document only that system, its control and the way in which you use the controls to improve your performance.
Then hope to find the right assessor. Do not create extra work (do work and then write about it; independent inspection).