First time discount discount
You can add a new customer group via Magento administrative area -> Customers -> Customer Groups -> Add New Customer Group
.
You can set a discount for a newly created group using Magento administrative area -> Promotions -> Catalog Price Rules -> Add New Rule
. On the creation page, using the "Customer groups" fields, you can select customer groups for which the promotion will be held. Enter other details, set the terms and conditions. Finally, click the "Save Rule" button.
Once the customer is registered, you can change your group via Magento administrative area -> Customers -> Manage Customers
. Click on the Edit link other than the client and change its group to Account Information -> Customer Group
. When you're ready, click the Save Client button.
source to share