I personally use straight vinegar in a spray bottle and I spray the branch till every bit of it is dripping wet with vinegar, leave it for a while then rinse it off well with clean water and sun dry. I like to wash the branch first with high pressure sprayer to remove dirt dust or other bits and pieces then do the vinegar.
Some people like to use bleach to kill anything harmful, then rinse well and dry well in sunshine.
I have also read that some people like to heat their branches/perches in a hot oven to kill everything.
All of the branches I use have come from my yard or from friends yards and I know they have no chemicals so I only need to wash to remove dirt, anything that wild birds/nature may have left on them will be killed with the vinegar.
I think there is a thread on here somewhere about disinfecting branches where everyone has pretty much said what their personal preferences are for this issue and why they do it the way they do.