A quick win I've seen and myself implemented as a consultant, is the use of correlationId in some form. If an incoming request has a correlation-id-header, then

A quick win I've seen and myself implemented as a consultant, is the use of correlationId in some form. If an incoming request has a correlation-id-header, then use it. If not generate a unique one. When calling other services make sure to include the current correlationId, and thus it spreads throughout the services for a given request. Most logging frameworks allow you to add something to every log message, so add the correlationId there. Then it's easy to track between multiple services. It also makes it easy to distinguish which log messages belong to a given request for a single service, so even without lots of services it can be a nice little feature.