Organisations are an effective mechanism to define the coordination model that structure agent interactions in Open MAS. Execution infrastructures mediate agents interactions while enforcing the rules imposed by the organisation. Although infrastructures usually provide open specifications to agents, understanding this specification and participating in the organisation could result a difficult task to agents, specially when the system is hybrid (i.e participants can be both human and software agents) and its specification becomes more and more complex. In this paper, we formalize an Assistance Infrastructure for Hybrid open MAS that helps agents to pursue their particular goals and, when they are aligned with global goals, lead to a better system's global performance. With this aim, we propose four advanced services (offered by the assistance infrastructure in a distributed way): (1) refined information, (2) justification, (3) advice and (4) estimation. We define two types of assistant agents. A Personal Assistant provides direct and sole support to one agent while a Group Assistant performs those complex processes which affect a group of participants with common services of interest.