The chess grand masters analyze hundreds and hundreds of chess games!
Constant studying of threads will give SD consultants the much needed "richness and density"...making them better consultants!
Below is a list of threads related to Returns. Study these regularly, make notes, do the practice in IDES and with time, you will become a MASTER!
1. Temporary issues after Go Live, how to design solutions for temporary issues?
Functionality - Reference mandatory
Understanding the issue - is it related to transaction data OR related to configuration?
SALES RETURN for the material sold before SAP implementation
2. Business user wants a different item category in RE order, not the default item category
Functionality - Billing relevance
Return Sales order - update of Item category change
3. Business does not want any major changes
Functionality - copy control
Userexit, enhancement
Propose order quantity in return sales order
4. View selected Order reasons in VA01/2
Functionality - make order reason a "mandatory" field in RE process, useful for reporting
Userexit, concept of Ztable (important and used frequently)
Order reason codes - specific to sales order type
User Exits In Sales Document Processing - System Modifications - SAP Library
Side comment: For a SD consultant to understand, identify the appropriate user exits that can be used for a requirement is very helpful.
5. Business process related ticket
How to handle "after" goods are returned to the company? Give credit to customer, supply the goods free of charge
Functionality - SDF, FoC
Sale return of Component of Fin Prod
6. Should returned goods be part of Salable stock or not?
Functionality - Movement type 651, 653
Return Delivery from Customer with Movement type 653 - Toolbox for IT Groups
Important - DN is the schedule line category provided for return process, in standard. VOV6
7. Business process and enterprise setup
Functionality - Enterprise structure > assignment > Sales org, distribution channel to delivering plant. An important step in SD
Intercompany Return Process Error
8. Pricing - what components to refund to customer? should tax component be refunded? should freight be refunded?
Functionality - Pricing
Side comment: In every aspect of SD design/tickets, mentally check - is there any impact on pricing?
9. Flow of goods in return direction, to which plant should goods be returned?
Functionality - Delivering plant (receiving)
Good example of a business requirement
10. Quantity in return order, compared to quantity in sales cycle
Return order with reference to the Billing Document
11. Business requirement
Implementing any thing...an entire process or one specific functionality, clearly understanding the requirement is very important.
Functionality - Implementation
In SCN, we have to understand based on reading the information. Read carefully!
Block sales order items for return orders
12. Functionality - Billing block
Generally in returns, credit, billing block is setup. Billing block can be setup at different levels (header, item) in RE order
Below thread touches on authorization also.
Unable to remove biling block return sales order
Important is to read the error message carefully, it gives clues, for solution
13. Functionality - REN, item category
Item category in a return order
Contest and a way to share knowledge -
If you find a thread which provides value to this document, please post it in your comments. I will add it; along with your name, as contributor 
Atregular intervals, I will update this blog with the "best" contributors
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