I'm new to RTM and was having difficulty remembering the formatting for the email body that allowed me to set different values in RTM. While I'm sure I'll get better with this over time I have setup an auto text item in Outlook that expands the items that can be set.

I tied it to the keyword RTM so if I'm sending an item to RTM now I just open the message and type RTM then hit F3.

RTM is then replaced with the following text block

Due:
Repeat:
Priority:
Estimate:
Tags:
Location:
URL:
List:
---
---
-end-

This helps me ensure I set the values I want to on tasks forwarded from email.