Before starting on your sketch, understand that it's important to know and master your tools well. If you do not know your tools well enough, your sketch will not turn out the way you want it. I can guarantee it. First, let's start by choosing some drawing paper for your sketch. A visit to the art supplies store will tell you that there's a wide range of art paper available. Some are multiple purpose drawing paper that you can use for pencil, charcoal, watercolor or paints. Those are more likely to be costlier.
However, if you're just going to do some practice sketches, all you need to have is a pad of smooth drawing paper. They don't have to be exceeding high quality but they do have to be smooth on the surface so that it's easier for you to blend. I've also noticed that smooth drawing paper have different grades. My advice is, choose something in between.
Once you have your drawing paper, you'll need to equip yourself with some pencils. I personally prefer to work with 2B to 8B pencils. These pencils give me a wide range of values and will allow me to create just about any effect I want.
You will also need some kneaded erasers. Kneaded erasers are dust free and behave like plasticine. You can pinch them into any shape you want and use it to ease off dark areas or create highlights in your drawing.
If you like, you can also get yourself a straight ruler and a circle template (for drawing round things), although this is not mandatory.