Depends on a bunch of factors, biggest being your path and if its coven or solitary. I'm guessing solitary, otherwise you would ask the coven. I did it on the full moon because that's what it said in my book [Wicca for Life by Raymond Buckland] but I know people who have done it on the new moon.
Be sure you are comfortable with the ceremony, it won't be the same if you're reading off a script, fidgeting, and second guessing yourself. Research different rituals to find the best one for you. Mine was nothing special, I used Bucklands as a guide, but mostly I spoke openly as to why I had chosen Wicca. Be sure to cleanse yourself and the area beforehand. Also, be sure you have everything before you close the circle. [You have no idea how many times my coven will reach for something mid-ritual only to realize its just outside the circle.] Is this at the beginning, middle, or end of your year and a day? Some people do three, two, or one, just curious because you should address your year and a day, either starting, how it is progressing, or what you have learned so far. I've noticed sincerity is very important in these solitary ceremonies because you are basically one on one with the Lord and Lady.