How to connect sharp edge with smooth one? For me, the hardest part is usually connecting creased edges with non creased (or sharp surface with smooth one). I am always trying to use proximity loops technique explained by Jonathan Williamson here:
https://www.youtube.com/watch?v=nBkwodrQq_4

Currently I am working on model in the picture below.
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What I need to achieve, is to have sharp edge at the place in green circle and smooth surface on the area in red circle. 


Topology details in edit mode. 


However with this kind of topology, the edge is sharp all along it's length. I am not sure if there is some plugin that can arrange edges so that even edges that are very close together can form smooth surface (something like circle in loop tools), calculating the adjacent edges.
All you need to do is separate the edge loops on the side you want smooth. Think of it as the opposite of proximity loops, where proximity loops make edges sharper, spreading out the edge loops will make it softer.

Simply select the vertices on the side you want smother, and press GG to edge slide them in to place.
If you get any shading artifacts, switch to side view and make sure all the edges and vertices are aligned. Scale to 0 on (an example) the Z axis to re-aline. For example, if you lowered one of the vertices, that will create a dip in the subdivided mesh and break the smooth look.

The vertices I moved are selected in this image.


Edited mesh in object mode