Assuming you are moving the only 2 NICs on your main Standard vSwitch, you will also need to consider migrating your Management VMkernel port. Any network change that causes the host to disconnect from vCenter will cause an automatic rollback, so you will need to ensure that there is at least one NIC connected to both the standard and distributed switches as you migrate the MGMT port. So the process would be as follows:
1) Add the host to the distributed switch
2) Create your distributed switch portgroups for VMs and any VMkernel ports you want attached to the dVS.
3) Migrate one of the physical NICs to the dVS to be used as an uplink
4) Once this is complete, migrate the MGMT port and any other VMkernel ports that require migration.
5) Migrate any VMs between standard portgroups and dVS portgroups.
6) Migrate teh 2nd physical NIC and add it as a 2nd uplink to the dVS
