How to draw guide

Step zero: Methods and posture
There's a reason why professional drawing tables look like this: https://s-media-cache-ak0.pinimg.com/736x/c0/95/e1/c095e1c3521cf12b40ad1e8eccd7a27c--a-drawing-drawing-board.jpg
It's ideal when the paper is slightly angled so that you are looking over it, but not casting your own shadow. This can't be done with digital tablets; you can't look at the surface you're drawing in, because of staring at the computer screen; you also can't angle the tablet as naturally or easily as you would a sheet of paper.
Essentially, drawing with a tablet is not great. Ideally, you'll pencil or ink your work "traditionally" before scanning it to add digital features. There are good, big tablets that feel exactly like a sheet of paper, but those are expensive.

Step one: Symbol Drawing.
This is why adults who have never practiced have the same skill level as children. It doesn't mean you're retarded, it just means your head is filled with the same symbols you used when you were little.
If you suffer from symbol drawing then it means you draw your idea of reality instead of what's actually there; you always do the same eyes, the same nose, etc. Rather than draw what your visual mind ACTUALLY sees, your logical mind says "I see a chair - here's my symbol for a chair."

Learning to copy is the most basic skill an artist needs. This is the first step towards analyzing references and other art to improve your own work.
One of the most famous exercises is drawing this Picasso upside down. Holding it upside down weakens the associations of the lines with the concepts. Why don't you try it right now? Grab a sheet of printer paper and a pencil.
https://usercontent1.hubstatic.com/9505680_f520.jpg
Here you go. Try to copy it to the best of your abilities and don't turn the paper until you are finished.
The point is to slowly begin drawing what you really see.

Step two: Construction
Construction is the skill of drawing anything from basic shapes, such as circles and squares. It's the magic behind drawing from imagination.
The most well known construction teacher is Andrew Loomis, but before jumping onto his long and intimidating manual here's a furry-friendly guide: http://www.lackadaisycats.com/howtodraw.php
This says more or less the same thing, but read it again: http://lackadaisy.foxprints.com/exhibit.php?exhibitid=356
Do you get the idea? Everything can be made wonderfully simple thanks to this.
Time for practice. Download http://www.alexhays.com/loomis/Andrew%20Loomis%20-%20Fun%20WIth%20a%20Pencil.pdf
and read up to page 20. Now I want to see you practice; draw a bunch of circles and construct anything from there.

A term to keep in mind: Chicken-scratch.
A typical beginner's mistake is the so-called chicken scratch, also known as a hairy line. This means drawing your lines with multiple short strokes instead of a long fluid stroke.
It's better to draw clean lines. Knowing where and how to draw your line is part of your basic drawing knowledge. Practice drawing long, steady lines with confidence. If unsure about your drawing, think about your next line placement instead of wildly guessing.
Of course, solid lines are drawn over an initial sketch (very important when doing line-art), but even the initial sketch should not suffer from chicken scratch. You can consider a sketch your art blueprint. You need clean lines for clarity.