Don’t be the one in the middle.
It was always clear that Putin was escalating in Syria to protect Russian strategic interests there and to impress the Russian people with his virility. Based on today’s news reports, it would also appear that he may have a larger aim–to force the US and its allies to back Assad by wiping out the non-ISIS opposition.
If what we are seeing today becomes a pattern, it may well be necessary for us to get international support for a no-fly zone over at least some portions of Syria that are held by parties other than the government and ISIS. That would force the Russians to choose to actually fight ISIS (which would be a plus), to risk a confrontation with superior US-backed forces, or to withdraw.