Have not done ODSP but helped a friend with disability app. As much specific info as possible. Write down things like meds, diagnosis and other info you may need to complete the applcation on a separate paper you can keep secure on you.
If possible, being able to take it home if it is extensive could be a help.
Dates you were under psychiatric care and the doctor(s) and therapist's name. Specific notes from doctors saying you are unable to work, and In Patient or out patient hospitalizations.
You can do yourself a service by providing detailed specific responses to questions that demonstrate clearly an inability to work.
Some people find the forums give them the compassion and empathy they seek.
http://forums.psychcentral.com
Please feel free to private message me or any of the Community Liaisons by left clicking on the name in blue to the left of their post) for questions or just to share.