Do you know that not all clowns WILL [accept an anemone as a host]? How long has the tank been up and running?
What type of lights do you have?
Based on reading some of his other posts, he doesn't plan on having enough light (i.e.: Fluorescent light $35) and I don't think his tank is set up yet.
Even under bad lighting the anemone should still last longer than 2 days. It may even last 2 months. If it died after 2 days it was sick anyway. So even under good conditions your anemone was already doomed.
Ocellaris and percula are notorious for being hard to host (and "hard" is a relative term because many other clown species will adopt a host within hours). If your have the right conditions and you really want the relationship of clown and host anemone, a clarkii clown is the easiest because it accepts every host anemone and sometimes anemone species that aren't (e.g.: condy), and it's very good at accepting the host immediately.
To answer your questions, you acclimate the anemone the same way you acclimate all other livestock and the best anemones for those species are the giant carpet and the ritteri anemone, neither of which is suitable for a 20 gallon tank.