How to Point Multiple Domain Names to One Website & How to Avoid Search Engine Problems

Hi BHW Members,
I want to register new domain name and pointed to my to my existing website
The new domain which is more relavant to my products.
I already worked hard for my current domain name for SEO,SEM
now if I pointed to my new register domain to my existing website how to avoide the seo problem?
Also how to do great seo for new domain name.
Need advice