Begin by sketching the main outlines lightly. I've shown the lines quite heavily here so that they will display on screen, but in a 'real' sketch I'd be drawing so lightly that you can barely see them. Use a very light touch, and dab with a kneadable eraser to remove excess graphite. Watercolour pencils do erase more easily than the standard waxy pencils, so you could use those directly for sketching, and so avoid having any grey graphite in your drawing if you wish. But do test them on a scrap piece first, as you'll want to be able to correct mistakes.
The great thing about sketching a plant is that there is a lot of room for error. Don't worry about making mistakes as the leaves curl into all kinds of shapes. Do try to get the Holly berries nice and smoothly rounded. If you do want to trace or use a grid, you'll find a large sized source image at the end of this tutorial, plus some links to other references.
Tip: If you are drawing a greeting card, make sure you have space at the left or top for the back of the card; it can help to draw a line where the fold will go so that you know how much space to use. Thick watercolour paper works well. Image Credit: This source image came from a creative commons collection that I've been unable to locate again, so I am presently unable to credit the photographer.