Need to know the following;
1. How does the branches connects to main office? Plain Internet, Internet + IPSEC, Internet +IPSEC/GRE, Plain Private WAN, Private WAN + IPSEC, Private WAN + IPSEC/GRE? If there is IPSEC or IPSEC/GRE, where thus IPSEC configured, router or firewall?
2. How does the main office and branch office network is setup? i.e. router<->firewall<->switch
3. What is the router model and IOS for the main office?
4. What are the most important traffic? i.e. mail, ftp, http. Most corporation the most important is mail. Put some number to tell which is most important to less important
Item 1 and 2 can be presented in a simple network diagram.
Need a proper placing for shaping, therefore those questions above are necessary to determine where to place the shaping. It depends on what you currently have, and sometimes what are you planning to do/have in the near future.