Hi,

this is absolutely easy

1. you need a few place which you really want see.
(Guidebooks, TV, Radio, Newspapers can give you inspirations)

2. you spot them on a general map. (now you splitted your route in small pieces)

3. Then you need detailed map(s) and guidebooks
You read every part of piece (2.) to check that's on the route I call them spots. (Take care for descriptions like "beautiful scenery", "nice road", etc.)
Then you choose small roads (mountains or river side what you prefer) and connect the spots to a route.

4. Finally you can use forums, the internet to get information about cycling paths, tips, etc.
(Then you can ask more detailed. How do come for A to B instead of nice routes of Poland)

Bye
Thomas