I use this method for digital drawing, but I learnt it from my aunt who's a traditional artist, so it can easily be transferred.
Now, as we all know, tracing a drawing is a Very Bad Thing. Which is why we, as artists, don't do that. But sometimes you really need to reference something to get it just right, and sometimes, no matter how much you look at the reference picture, it still doesn't get right. And this is where the grid method comes in.
Say you want to draw a duck. You've never drawn a duck before in your life, but now you need it for something or another. What do you do first? You find a reference picture of a duck.
My very own duck picture. Copyright me, etc. etc.
After finding the reference picture, it's time for the grid. Make a grid on top of your reference picture, like this:
Now, once you've done that, you make the same grid in a different canvas. One without the reference picture in it. Like this:
Then you put the two images next to each other so that you can see both, like this:
And then you start drawing using the grid as points of reference. In the end, you'll hopefully have a result that looks quite a bit like the picture you chose.
And that, my dears, is the grid method. Now, I'm sure some of you have done something similar as children, and as you can see, it's still applicable. Wonderful lineart, no tracing. Grids are also very useful if you want to make an image larger or smaller. Just change the size of the grid on the canvas you're drawing in.
Now, make sure to keep in mind the difference between Copying vs fanart & referencing, and as a good sport, always credit your references. Now go forth and make grids like shiny happy artsy people!