Integrating Quality, Environmental and Health & Safety requirements into a single management system can be a formidable task, so having a clear and practical plan on how to achieve this is a pre-requisite to success. Having assisted numerous companies to implement integrated systems and having audited scores more, I have concluded that the best and easiest to follow implementation programme is one based on the process approach which is intrinsic to the ISO9001 quality standard.
Start first by identifying those business processes that you follow to convert customer requirements into delivered products and services. The standard refers to these as "product realisation" processes. Then identify those additional processes that you employ to support these activities and maintain your systems and facilities e.g. IT and site maintenance, vehicle maintenance etc.
Think about how these processes inter-act and inter-relate to each other and show this in a top level process map. The next stage is to review the standard and identify those management processes that you use to control the work environment and ensure that everyone is pulling in the same direction.
All organisations have product or service realisation processes if they are trading and serving customers, but when starting out, it is unlikely that you will have introduced all the management processes to the degree of formality required by the management system standards.
A review of the three standards ISO9001, ISO14001 and OHSAS18001, will reveal that most of these management requirements are similar in nature (often having the same titles although related to different disciplines) Example: management review, internal audits, corrective actions, preventive actions etc.
Now you need to consider how these impact on the business processes, and include in your top level process map or in a "management processes" map.
Many of the requirements in one of the standards will have parallels within the other standards, although in one or more of the standards they maybe more demanding. ISO14001 has requirements for aspects and impacts analysis which is just another term for risk assessment, which is also a work planning requirement for health and safety. Consultation and communication and competence and training are also requirements of all three standards to a greater or lesser extent.
Using your top level process maps you can identify how other requirements of the three standards fit in to the business, its products and processes. You can then link these in, as processes in their own right or as sub-processes or supporting processes.