A will give you a nice tips for creating isometrics, you will need for this:
1 paper page with isometric grid
2 white papers for drawings
1 pencil
1 felt pen (black is better)
A light table
A scanner
And photoshop
Steps.
-Create a isometric grid in paper, use it over a light table (Easy to make) and stick it, use a white page for draw your asset over it, and draw it using a pencil over the grid reference page, next, use another white page over the new pencil one and follow your lines whit a felt marker, remenber black is better,this is a cleanup of your previous sketch, now you have a clean copy of your pencil concept, right? -Well now scan your draw with your scanner of course.
-Import the file in Photoshop.
-Duplicate the layer
-Set the blending mode for the upper layer in Multiply
-In the lower layer colorize you drawing (the upper layer will respect your trace)
-After finish the color, save in your preference format.
Hope this help to someone.
Bye