Wait!! Before you throw that drawing in the bin!!!!!
You have been drawing for hours, but the drawing doesn't feel right. You are quite frustrated, but before you just scream, and curl the paper togehter, throwing it in the garbage bin, wait a minute:-) Take a deep breath, maybe a cup of coffee, stretch your legs, jump a little, talk with somebody.
After this little break, return to your drawing, and have another look. Take a deep breath again. Now ask yourself what you like about your drawing, and what you don't like. How could you change it now, when it's almost done? Is it only a small correction or do you need to do some serious redesigning? If you can't come up with anything now, take a look at my list. "Before you throw your drawing in the bin"
Before you throw your drawing in the bin:
Take another element and place it, so it will cover the area you don't like. You can use a white acrylic marker or a white piece of paper. If you want color, use a colored piece of paper, or a colored acrylic marker. Of course you can use whatever tool you like, as long as it cover up the problem area.
Cut out the element/elements you like, and place it on another paper. If you need more space, choose a bigger paper. You can now use it as it is, or you can continue to work with this new setup.
If you only use pencil or pen, spice it up by using another tool. You can use watercolor, acrylic markers, chalk, or goauche. Try out different tools, turn your failed drawing into an experiment. It can be much easier to expand your limits and try something new on a piece of paper that's not completely blank. And the experiment might turn into something unexpected and interesting. (If you use gouache, or watercolor it's important that your paper is thick quality paper at least 220 gram.)
If you just can't make it work, take some white gouache or white acrylic marker, and make a thin layer which cover it all up. Now you have a new surface, where you can still have a glimpse of the old drawing. On top of that you can create something new, while keeping the history of the process, which gives a nice layer effect. (If you use gouache, or watercolor it's important that your paper is thick quality paper at least 220 gram.)
Another radical solution is to cut it all up in pieces. use them as mosaic elements on another drawing, or place them in a box with pieces of paper, you never know when you will need it.