I wasn't very good with pixel art until I got to thinking. Seeing as how I use MCEdit quite a lot for my projects, I have become dependent on the program. And since I am so good with MCEdit I will share with you my ideas on how make pixel are fairly quickly! **Can't guarantee this will help you but it's just a starting point for those who are struggling with pixel art like I was**

1. First off you need to get MCEdit (or some other Minecraft world save editor).
   
2. Then simply google a picture or upload your own to your computer and open it in something like paint or fotoshop!
   
3. [This step is optional] Once you do that, simply resize the picture to the desired size. (for paint, once you do this you should hit crop if you make the picture smaller.)
   
4. Zoom in on the picture till you can see each of the individual pixels clearly
   
5. Open up MCEdit (or whatever Minecraft world save editor you have)
   
6. Open a world save that is fairly flat (I personally prefer using pre-made flat maps at the bedrock layer for more room to work with.)
   
7. Once you have the world save open on MCEdit, create a 1 block thick working space out of something like wool that is as many blocks tall and wide as the picture itself (treat each pixel as if it were one block in minecraft). (If you have a picture taller than 128 pixels it is recommended that you place this working space flat on the ground and not vertically)
   
8. Then start going through each line/column of blocks in MCEdit and replace the wool with the same color of the corresponding pixel in the picture.
   
9. Keep doing this until you have made the picture you wish to create in minecraft.
   

This technique may be time-taking but it will save you at least 15% of the time that you were originally using to build it block by block in minecraft directly if you were doing it by yourself!
Hope this helped and good luck with building your pixel art projects now!