Regardless of style and media, not only art but every complex thing (the result of multiple pieces together) that humans build follow a similar process.
Doing loose pieces without a scene set up is like focusing on details after getting the general picture.
We have the illusion that jumping in and do things without a base is faster but we can get lost, redo and spend much more time than necessary.
After you know the setting and kind of environment, first start with sketches. "Scenes" in small rectangles.
I didn't even spend two minutes on each one.
Btw, this is how I design multiple scenes in the same level:
http://i.imgur.com/fI2k9ho.jpgThem sketch the pieces. Props, builds, animals, NPCs, plants, optional stuff, etc. Again, a few minutes for each one.
Broken, small, no much detail.
Something you would never show in your portfolio but is the first stage of the work.
My sketchbooks are filled with pages like that and some looking even more worse.
We usually only see fancy concept arts and this give a wrong impression of actual production art for most people.
Now do a mockup. How would the scene looks like if you had a screenshot of it?
Nothing big (in a smaller scale than in-game) nor precise, just a sketch painting to set up color, mood and what you have to achieve.
This is also the time for the fancy concept arts if you want to design things better.
There are no complex objects in this scene so the mockup was enough.
Then start to create the actual sprites.
Don't do one at time but many sketches then many fill coloring then many detailing.
I don't tell you to do everything at once because expecting you will know everything you need to do and everything will work beforehand is unrealistic (mainly because tiles, they need a lot of try and error). Work in batches.
This is the result:
I always make tilesets with this process and take a few days for each scene.
Another mockup example of a "more tile-based" scene:
http://i.imgur.com/mCgG9oJ.jpgFor me everything after the sketch is details and you should not spend time until this point.
The purpose of game art is to decorate things. It can add mood, interest and fun but can't change or fix game mechanics by itself.
In order to save even more time, in theory, you could draw a simple subdivided rectangle, call it a house and when the programmer is done with the collision code and testing, you decorate the rectangle to looks like an actual house, animate birds in the roof, create reflection shader for the windows and so on.
You avoid redoing things that looked good but didn't fit at runtime.
After all redo sketches of a few minutes is better than redo 8+ hours of finished art.
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