A simple, easy method for this is to extend out your arm and pointer finger. Pointing at the ground visualize a beam of light shooting out and touching on the ground where you point. Turn in a complete circle; the beam constantly shooting out of your finger, and when you make a full circle you have cast your circle. You could also use a wand. I've heard of some people using an athame for this process (though I am sure some one may find that as an improper usage of the tool)
You could just visualize your circle around you. The only downfall with this is that you would need to keep constant at visualizing the circle to keep it up and working. Unless your good enough with this to only consciously visualize it being there and then your subconscious mind taking care of keeping it up and working.
Another method is by starting at facing the North, South, Easy, or West (starting point is debatable but what matters is making the full circle) and then calling upon the element of that quarter. Keeping going round and calling upon the elements until you make the full circle and you're back at the starting point. At each quarter you could ask the elements to not only add their part fort the circle but also stuff like protection, aid in your magickal workings, extra energy, etc. It's how you want it to be. (Though some people would debate that you call upon them for a specific reason in a specific way)
You could also do a more physical, tangible, human eye visible circle. Make a circle with stuff like chalk, salt, rocks, candles, or sticks.
It is debatable as to which way you turn making the circle. Some say clockwise to make and counter to break. I personally don't see a difference in whether you turn left or right. It's what you're comfortable with doing. What works best for you. Just as long as you make the full circle. And when you make the circle you want to make it so you have plenty of room to get done what all you need or intend to do.