So you think you can't draw horses?
Think you can't draw faces? Hands? Buildings? 3D objects? WATER?
Well yes you can, and I will tell you (and later show you) how.
The technique is very simple, almost too simple. But, granted, it takes a bit of training and practicing still - but its a powerful tool and won't take much explaining.
This is the technique to draw anything you see - anything at all. Put all that stigma away, all that baggage that says you're not good at drawing, and replace it with "this is how I will learn to draw".
Sit down and get comfortable, find a place where you can easily see things around you, but are able to draw. Have a hard surface under your paper, and keep the paper steady. Now grab a ruler and place in front of you anything you'd like to draw - a vase full of complicated flowers, a moose skull (why the hell do you have that?), and vase and candle, whatever you want.
Now pick a point in space - an imaginary point in your subject matter, preferably a corner. Just imagine that as an anchor, that is where you'r going to build your picture from. Here is where the technique comes;
hold out your ruler at arms length and measure from that point to any other interesting, exciting, or unique point in space. It could be from the bottom of the vase to the top, for an example. Now take your ruler back to your paper and draw a light line that is equal in length and direction. (If you're paper is too small, divide the distance by half).
At this point you should have a nearly perfect length of the vase drawn on your paper (as an example). From here on out you will just be repeating this step, using starting points and ending points, but always have the starting connected to some point. When you first start out, go CRAZY with lines. When you stop, and are done, you should only see LINES LINES LINES LINES. Not only does this look cool by itself, if you look closely at your paper and the subject matter you should be able to see that they are very similar in size and shape (details omitted, of course).
To do this by hand is very difficult, but if you master this technique it will come with time.
Now that you have your crazy line drawing, start involving detail in the drawing - start adding the actual curvature of the base of the vase into the base of your drawing. You know the length already, now you just need to add in the curves. The most important thing here is : DRAW WHAT YOU SEE. Most people when they draw subject matter in front of them aren't drawing what they see. They are drawing what they think they are seeing.
For example if you put a coffee cup in front of a 4th grader and ask her to draw it, she will not draw what she sees, she will draw a coffee cup, any coffee cup - one she made up in her head. If there is a star on the coffee cup, she will make her 5-sided star and add it to the cup, even if there is a 6 sided star on the cup! (This is just an example, maybe the kids a genius and floors you with her talent).
When you see something, don't think about what it is. ONLY draw the lines that exist. Forget about the bias of it being a vase, or a flower, or a skull. Don't focus on what these things are, only see the lines - the shapes that are made from their form. This will unbias the mind and allow for the best benefit.
As you add more and more detail stop and look at both the subject and your drawing - does everything look OK? Are some of the angles too sharp or wide? Are some things too long? Does it just look...off? Then erase and try again, keeping in mind the anchor points and lines you put in before, maybe you'll have to redo those as well.
Don't draw what you THINK you see. Draw only what you see.