Sadly, there isn't an exact formula that covers all scenarios. I use an excel spreadsheet that tracks the creditor, balance and drop date for each, and that really helped me decide which coarse of action to take for each one. Then I typed each action into the record and logged the result of that action when it occurred. I pasted a copy (sort of) of this sheet on the boards when I started and it helped others give me advice on what to do. I encourage you to try something like that to help you line up your ducks. 
Here's the flowchart:
