Of the two methods I use the first involves casting a circle with my athame, invoking the elements at their corresponding corners and drawing a pentagram over my heart. The second is using visualisation and this is used where physical movements may not be appropriate. I encase my self in a cocoon of white light and again a pentagram over my heart. Your method may be different to mine but if you are a beginner this is a good place to start.
Your circle must consist of energy that you feel comfortable with and feel protected by. In your visualisation is may take any form that feels right eg. Simple white light, flames or a web. It must be impenetrable to any harmful energy. You can also use a physical substance like chalk, flour or salt to give it tangibility if you are not completely comfortable with only the visualisation. This may not be appropriate depending on your ritual location.