Voice Assistants (VAs) bring various benefits for users and are increasingly popular, but some barriers for VA adoption and usage still prevail, such as users attitudes, privacy concerns, and negative perceptions towards these systems. An approach to mitigating such obstacles and leveraging voice interactions may be understanding users mental models of VAs, since studies indicate that users understandings of VAs are unaligned with these systems actual capabilities. Thus, considering the importance of a correct mental model for interactions, exploring influential factors causing misperceptions and solutions to deal with this issue may be paramount. The objective of this research was to identify leading causes of users misperceptions and offer design recommendations for aligning users mental models of VAs with these systems real capacities. In order to achieve this goal, we conducted a systematic literature review (SLR), exploratory interviews with experts, and a questionnaire-based three-round Delphi study. The results indicate that design aspects such as VAs high humanness and the lack of outputs transparency are influential for mental models. Despite the indication that these drivers lead to users misperceptions, removing VAs humanness and excessively displaying information about VAs might not be an immediate solution. In turn, developers should assess the context and task domains in which the VA will be used to guide design decisions. Moreover, developers should understand the users profiles and backgrounds to adjust interactions, as users characteristics are influential for how they perceive the product. Finally, developing teams should have a correct and homogeneous understanding of VAs and possess the necessary knowledge to employ solutions properly. This latter requirement is challenging since VAs novelty might demand professionals to master new skills and tools.