Lets break this down:

1. Register as a company – this costs very little and provides greater security than operating as a sole-trader or in a partnership
2. Ensure your company is complying with IRD - register for GST if you expect to earn more than $60,000 and ensure you have your own IRD number when operating as a company
3. Get insurance! Preferably both public liability and professional indemnity insurance
4. Put aside a conservative amount of money from your income for tax
5. Get an accountant – as a contractor you deduct your own PAYE, are liable for paying the GST that you receive, and are able to claim back your GST. An accountant can ensure that all your ducks are in a row so that you can get back to what you do best!
6. Set up an invoice template to make it easy for you and for the companies who contract you. Xero have invoice templates you can use! However, if you prefer to make your own, be sure to include key information such as your name (and your company name), your GST number, your bank account details, the hours worked and your rate along with a total including GST. 
7. Having a rainy day savings account is useful, this will help to cover leave or time in between contracts
8. Lastly, use a recruitment company like one eighty to ensure a steady flow of work!

As always, feel free to contact us for more information.