There are a lot of approaches you can take to drawing what you want. For instance, if you look at a chair you can try to draw the shape of the negative spaces, such as what you see between two of the legs. If you want to draw a tree first look at the proportions of leaf masses to trunk, and of the masses of leaves to each other. Then look at the silhouette of the tree, the dark and light values, and the textures.
In drawing a human there is more than one way to get to where you want to go. Some artists use projectors, and some use tracing paper. A book on drawing might tell you that if you want to draw a portrait then start by drawing a slightly egg shaped oval, divide it up with lines according to the proportions, and then to gradually erase a re-draw each part to make it look more like your subject. Then you render the values areas and textures. This method is kind of working from the outside in, like the tree I described above. However this approach involves a lot of erasing , and the more you erase the more damage you might do to your paper, and a lot of erasing limits what you can do in drawing on top of a colored background, and so on. Some people will literally erase a hole in their drawing paper.
Another approach is to draw from the inside out. Choose a sharp photo of a face where you can see the eyes clearly. If you look at the inside corners of the eyes examine the negative space in between them. If you print out your picture on plain paper you can put a dot there at the eye comers with a pen. Now if you look directly below those two dots you can put two more dots at the bottom sides of the nose by the nostrils. What those four dots picture is the four corners of a rectangle where it is a little longer than it is wide. The ratio is usually about 3 wide to 4 long. From there you can look at the proportions outward, put dots there and connect them up. The distance from the inside corners of the eyes to the outside corners of the eyes is similar to the distance between the two inside corners. Put dots at the beginning and end of the eyebrows and at the top of the peak. So put dots there. Put a dot at the bottom center of the nose. The distance to the mouth line from the bottom of the nose is about half of the length of the nose. The distance from the mouth line to the bottom of the chin is about the same as the length of the nose. Now look at the shape of the chin, the shape of the jaw line, the hair line, where the bottom and top of the ears come to compared to the rest of the face. You might notice that on a pretty, well proportioned face the distance from the chin to the bottom of the nose, from there to the eyebrows, and from the eyebrows to the hair line, is about the same, If the face is level in relation to you.
You can draw anything you want from any photo printed out on plain paper by the following method. Draw as large a square as you can on the photograph. Then connect the corners with an X . Use the center of the X to divide it up into four squares, and draw X's to connect their corners. When you have a number of squares you line up their centers and continue the pattern outside of the original square to cover the whole picture. You can grid it a little smaller in areas where you need more detail like the face and hands and grid it larger in areas where there is less detail. You can also put a dot on the most important points where you have to be precise, like the corners of the eyes and the edges of the irises. Then measure the dots from the nearest grid corner. The eyes are the single most important part of any portrait where they appear. Then draw the same grid pattern lightly, and I mean lightly, on the drawing paper to whatever size you need. It may help to label the the rows and columns with letters and numbers respectively to help keep it straight. Then just draw what you see from one triangle area to the other. You need to carefully erase the grid before you get too far . Then when you get the basics drawn why not go back to your reference picture and draw contour lines around the different value areas on the face, in the hair, and so forth. Then work on putting in the value areas in your picture with pencils with h leads (hard) for light areas, and b leads (soft) for dark areas. The ebony pencil is best for the darkest areas. You can use paper stomps, tissues, artist's chamois, and your fingers to smooth out the transition areas or little value patches. Be sure and wash your hands often with a degreaser like Dawn to keep oil of the paper. Use a soft white eraser to make little changes, and you can use ink too if you want on black areas, but be careful not to do it in large areas or the difference will be obvious.
I use mechanical pencils to start with and then add more pencils later. The most common beginner mistake is to try and draw the hair as individual strands instead of looking for patterns and texture. Also draw everything lightly and then darken it later, you don't want your lines to show in your final drawing. Here is a drawing I did of Alyson Michalka:
http://www.artwanted.com/imageview.cfm?id=838192
And here is the best explanation on the net on how to draw hair:
http://www.rebekahlynn.com/free/tutorial/hair_tutorial.html