This page helps you calculate trigger and revert values for pre-FEC BER based proactive routing.
Input the FEC limit of your card (should say in data sheet or similar). Then put in the margin you want to the trigger and finally to the revert value.
Cisco calls it dbQ margin whereas Juniper calls it Q2-factor.
I'm using an example of 2dBQ margin for trigger and 3dbQ for revert. You should probably figure out what's good for your environment but this is a start.
FEC limit: BER
Trigger: dbQ / Q2-factor
Revert: dBQ / Q2-factor
FEC limit dbQ:
You can read more about this over on Juniper's page.