If you're completing the forms yourself I would say don't over complicate things. If your dad trusts you to act in his best interests leave all the sections about special instructions blank. Your dad will need to complete (and sign) one of the options about whether or not he wants to give you authority to give or refuse consent to life sustaining treatment, but other than that try and keep it simple.
The obvious advice is to make sure all names, addresses and dates of birth etc. are correct as once it's registered these can't be corrected. Make sure that the correct dates are put in and in the correct order. The donor (your dad) should sign first, then the certificate provider, then the attorneys and then the application to register. You can date it all the same date if you all sign on the same date, but if, for example, the date the attorneys sign is before the date the certificate provider signs it will be rejected.
The signatures of the donor and the attorneys must be witnessed. Read the instructions about who can be a witness carefully.
If you take your time and read the notes carefully it is relatively straightforward, but as always you should consider taking professional legal advice.