I would start at one end and work all the way through. If some sensors are soot-fouled, it's likely they all, or most are. Don't use high pressure/velocity fluid or air on the sensors, such as blasting them out with 150 PSI shop air. If you use the aerosol O2 sensor cleaner, let them drip/air dry after a thorough flushing. Some DIY methods suggest using a solvent sprayer (that uses shop air), but I think it's too much. Air brush sprayers work well, though.