Practice and patience. Most people give up too soon and assume that they aren't good at drawing. I did that for the longest time until I set my mind to it. It turns out that I'm actually good at drawing. The only thing I found I'm not the best at is drawing people, I'm usually not successful in drawing faces. However I've been getting better and I'm not giving up. I practice a little bit each day. hope this helped you :)
Step one: Learn from good source such as http://www.drawspace.com/. It is a good free source for drawing. Step two: Observe and Practice all the time. Observation lets you learn how to analyze and draw shapes and effects and you can practice by drawing from what you see. This will help you to learn how to create shades, light, and different styles.
Practice and observation :) Improvement can be a slow and painful process but if you practice you will see changes. What are you drawing? Animals? People? Study anatomy and proportions of living beings. Find some artists that you like. Observe how they draw. What style(s) do they use? Find a style that suits you.
Observation, practice, and study; try looking at several different art styles and find your own from it. The best ways are looking at art books and practicing techniques from them or from looking at guides online. Otherwise, study real life photos and use them as your inspiration, but never try to copy someone else directly or you won't find your own style. :) Hope this helps!
You practice! Practice makes perfect. Start by working on things you have problems with or you think could be better. You might get frustrated and feel you aren't getting any where, that happens but you have to keep trying! With time you should see results! Promise ya!
Sketch lightly on the things that look hard and don't stress to hard on your art work just let the pen,pencil,paintbrush whatever you use flow lightly in your hand and practice making things the right shape DETAILS ALWAYS LAST :3